I think we should be discussing more observations on the stages rather than what simply should and should not be banned.
Battlefield - Flat surface with multiple platforms. The bottom curves up, aiding recovery. Nothing stands out to give any one character an advantage over another. I think everyone agrees should be neutral.
Final Destination - Completely flat. Edge hangs out, gimping some recovery. Everyone also agrees this should be neutral.
Delfino Plaza - Each stop offers different advantages to different characters. The moving platform is basic, almost battlefield-like. First stop is the mound of earth with water as pits. Seems rather neutral. Second stop is three small rectangles of earth with water as pits. It seems to favor an aerial game more than anything. Third stop has a very small wall I don't think will be exploitable. It has walk off ledges. Fourth stop has walk off ledges probably more dangerous than the third since it has a dip rather than the wall. Fifth stop is a flat platform with water at the ends. Final Destination-like. Also noteworthy is that the stage switching happens slowly and is unlikely to cause someone's death. I would doubt any three-stock would go any longer than those. In my opinion, it should be neutral. All the stops are short enough to not be drastically advantageous to either side.
Luigi's Mansion - The floor of the second story is two-thirds solid, and would create a mini-cave of life. Destroying the pillar on the first floor would get rid of that. The pillars hinder projectiles, but they can be destroyed. You can't really camp in any certain section since the pillars can be destroyed away from you. I see no reason for this stage to be banned. The hindrance of projectiles might cause it to be counterpick, but I would think either counterpick or neutral would be valid.
Mushroomy Kingdom 1-1 - Short ceiling. The slow scrolling is not inherently flawed, but the large amount of walls could very easily lead to infinite combos causing KOs. I don't see this being neutral. I don't like to say stages should be outright banned one week after the game came out, so I would lean toward counterpick, with the possibility of being banned.
Mushroomy Kingdom 1-2 - Massive cave of life. Only real KO possibility is to the left side. It also has a good amount of walls that could possibly lead to infinite KOs. I'm much more inclined to consider this stage banned.
As a note on these two stages. You can ban one while having the other be counterpick. You would simply decide upon 1-1 and then if the stages is 1-2, immediately cancel the match and try again. Realistically this would only have to be tried three or four times max, and would not take much time at all.
Mario Circuit - The cars have no real KO ability except at very large percentages. There is a map on the back of the stage and arrows that alert you when cars are near. They are a non-issue. Both the top and bottom have walk-off ledges. The top might not be as bad since you can stay in the middle platform, but D3 could potentially chain grab you for a KO anywhere else. That alone would keep it from being neutral in my opinion. Whether it is counterpick or banned will most likely depend on more information being discovered about the limits of D3's chain grab.
Rumble Falls – Slow scrolling most of the time. There is a wall a few seconds up but I due to the nature of the stage I doubt anything would be exploitable, at least not for any length of time. There is one spike that can kill as low as 30%. The spikes a bit further up can kill off the top at fairly low percentages when they first appear. There are a few walls that could lead to KOs. Characters with low jumping ability are disadvantaged, keeping the stage from neutral in my opinion. Since it scrolls slowly and is highly predictable I don’t think that will be a big concern. I think the biggest issue that might lead to its being banned is the spikes and their ability to kill very easily. I would say counterpick for now.
Bridge of Eldin – Not much to say here. King Bulbin is highly predictable and does not have very much KO ability. The bomb is obvious after he charges across. The walk-off edges could lead to D3 chain-grab KOs. That would keep it from being neutral, and once again we would need to wait for more information regarding any ways to break D3s chain grab, either through character choice or actual abilities, before completely banning it.
Pirate Ship – All the obstacles are very predictable. The catapult is visible for a good while before it shoots. The bombs are slow and you can predict where they are going to land, although they do have decent KO ability. The wind is obvious. There is a visual and audio notice before it hits the rock. I see no reason for this stage to be banned.
This is taking me awhile to type up as I’m playing matches as I write this to make sure it is accurate, so I will type more stages later today or tomorrow. I think I can say with a certainty that Warioware Inc. and Mario Bros. should be banned due to their unusual nature. From what I’ve seen, New Pork City and Flat Zone 2 should also be banned. 75m possibly as well for the same reason as New Pork City. I’m going to refrain from making any other judgments until later.
Battlefield - Flat surface with multiple platforms. The bottom curves up, aiding recovery. Nothing stands out to give any one character an advantage over another. I think everyone agrees should be neutral.
Final Destination - Completely flat. Edge hangs out, gimping some recovery. Everyone also agrees this should be neutral.
Delfino Plaza - Each stop offers different advantages to different characters. The moving platform is basic, almost battlefield-like. First stop is the mound of earth with water as pits. Seems rather neutral. Second stop is three small rectangles of earth with water as pits. It seems to favor an aerial game more than anything. Third stop has a very small wall I don't think will be exploitable. It has walk off ledges. Fourth stop has walk off ledges probably more dangerous than the third since it has a dip rather than the wall. Fifth stop is a flat platform with water at the ends. Final Destination-like. Also noteworthy is that the stage switching happens slowly and is unlikely to cause someone's death. I would doubt any three-stock would go any longer than those. In my opinion, it should be neutral. All the stops are short enough to not be drastically advantageous to either side.
Luigi's Mansion - The floor of the second story is two-thirds solid, and would create a mini-cave of life. Destroying the pillar on the first floor would get rid of that. The pillars hinder projectiles, but they can be destroyed. You can't really camp in any certain section since the pillars can be destroyed away from you. I see no reason for this stage to be banned. The hindrance of projectiles might cause it to be counterpick, but I would think either counterpick or neutral would be valid.
Mushroomy Kingdom 1-1 - Short ceiling. The slow scrolling is not inherently flawed, but the large amount of walls could very easily lead to infinite combos causing KOs. I don't see this being neutral. I don't like to say stages should be outright banned one week after the game came out, so I would lean toward counterpick, with the possibility of being banned.
Mushroomy Kingdom 1-2 - Massive cave of life. Only real KO possibility is to the left side. It also has a good amount of walls that could possibly lead to infinite KOs. I'm much more inclined to consider this stage banned.
As a note on these two stages. You can ban one while having the other be counterpick. You would simply decide upon 1-1 and then if the stages is 1-2, immediately cancel the match and try again. Realistically this would only have to be tried three or four times max, and would not take much time at all.
Mario Circuit - The cars have no real KO ability except at very large percentages. There is a map on the back of the stage and arrows that alert you when cars are near. They are a non-issue. Both the top and bottom have walk-off ledges. The top might not be as bad since you can stay in the middle platform, but D3 could potentially chain grab you for a KO anywhere else. That alone would keep it from being neutral in my opinion. Whether it is counterpick or banned will most likely depend on more information being discovered about the limits of D3's chain grab.
Rumble Falls – Slow scrolling most of the time. There is a wall a few seconds up but I due to the nature of the stage I doubt anything would be exploitable, at least not for any length of time. There is one spike that can kill as low as 30%. The spikes a bit further up can kill off the top at fairly low percentages when they first appear. There are a few walls that could lead to KOs. Characters with low jumping ability are disadvantaged, keeping the stage from neutral in my opinion. Since it scrolls slowly and is highly predictable I don’t think that will be a big concern. I think the biggest issue that might lead to its being banned is the spikes and their ability to kill very easily. I would say counterpick for now.
Bridge of Eldin – Not much to say here. King Bulbin is highly predictable and does not have very much KO ability. The bomb is obvious after he charges across. The walk-off edges could lead to D3 chain-grab KOs. That would keep it from being neutral, and once again we would need to wait for more information regarding any ways to break D3s chain grab, either through character choice or actual abilities, before completely banning it.
Pirate Ship – All the obstacles are very predictable. The catapult is visible for a good while before it shoots. The bombs are slow and you can predict where they are going to land, although they do have decent KO ability. The wind is obvious. There is a visual and audio notice before it hits the rock. I see no reason for this stage to be banned.
This is taking me awhile to type up as I’m playing matches as I write this to make sure it is accurate, so I will type more stages later today or tomorrow. I think I can say with a certainty that Warioware Inc. and Mario Bros. should be banned due to their unusual nature. From what I’ve seen, New Pork City and Flat Zone 2 should also be banned. 75m possibly as well for the same reason as New Pork City. I’m going to refrain from making any other judgments until later.