I went ahead and made a list of stages in approximate order of how "neutral" they are for a standard 1v1 tournament. When making this list, I was considering the following things: (A) how fair it is to all characters. (B) how "stupid" the stage is... i.e. how likely it is that the stage will kill a player OR save them when they would die on another stage (the "cave of life" clause). (C) walkoffs... I'm mixed on this one, but I do feel that walk-offs promote degenerate play and remove one of the most interesting interactions in Smash (edgeguarding), so I biased the list heavily against all permanent walkoffs. (D) tournament timing... this is actually a huge one for me. We don't want matches timing out every game, so big stages or camping-friendly stages should be looked at skeptically.
Smashville
Battlefield
Final Destination
Lylat Cruise
Kongo Jungle 64
Town and City
Duck Hunt
Castle Siege
Skyloft
Halberd
Delfino Plaza
Wuhu Island
Luigi's Mansion (destroyable caves of life. mildly one-sided toward/against some chars)
Windy Hill Zone (similar to wooly. Big stage with a bit of stupid in the asymmetry, gravity, and springs)
Mario Circuit (Pretty fair but toeing that stupid line with stage kills, ceiling, etc)
Garden of Hope (easily avoidable crab, destructible terrain doesn't do much. Only issue I see is the dropping platforms)
Pokémon Stadium 2 (technically fair. That wind transformation completely changes the match however, which I dislike)
Norfair (predictable hazards, multiple grabbable ledges, and camping is promoted)
Woolly World (big stage with walkoffs, dropping platforms, caves of life, etc. Technically fair but somewhat dumb)
Mushroom Kingdom U (Nabbit is stupidly annoying. The spiny fish can kill. I just can't see a serious match here)
Orbital Gate Assault (More hazards than most stages, strange platform layouts. Transitions can screw certain chars)
Kalos Pokémon League (I actually consider this stage fair... but the hazards and metal just tip the 'dumb' scale)
Pilotwings (I was on the fence about the cave hitting you... the camping makes it pretty bad)
Wrecking Crew (Circle camping galore... otherwise I like the stage)
Big Battlefield (I really don't think this is viable or necessary for a 1v1... too big, campy, etc)
Skyworld (Cave of life... no edges when destroyed... other random hijinks, etc)
Port Town Aero Dive ("alright I'm winning!" Invisible car hit > dead... : / )
Mario Galaxy (Permanent walkoff and very big)
Coliseum (Permanent walkoff and very big)
Boxing Ring (Permanent walkoff, light camping, and very big)
Wii Fit Studio (Permanent walkoff and big)
Gamer (Mom = random and OP)
Onett (Permanent walkoff and car shenanigans)
Yoshi's Island (Permanent walkoff and spin block/hill shenanigans)
Bridge of Eldin (Permanent walkoff and super campy)
Mario Circuit (Brawl) (Permanent walkoff and kart shenanigans)
Pac-Land (Permanent scrolling walkoff and just annoying in general)
Flat Zone X (Permanent walkoff and stage hates you)
Gaur Plain (Permanent walkoff and you hate stage)
Wily Castle (would be great if yellow devil weren't around)
Pyrosphere (I seriously....seriously wish I could make a case for this stage to be legal)
Temple
Jungle Hijinxs
75m
Palutena's Temple
The Great Cave Offensive
ok so a few notes on this list. If it wasn't obvious, green = little reason to ban ever, yellow has potential, orange has less potential, and red is lol
Yes I consider KJ64 more neutral than T&C and Duck Hunt, especially when you consider that Smashville is going to be a neutral always. KJ64 has a lasting negative bias for being too big but that's actually a mostly non-issue in this game, and T&C is arguably as big/camp-friendly. The valid arguments against KJ64 are the pass-thru floor and barrel, but I also don't find these unfair. When you consider a striking process, I would rather have to strike KJ64 than have to strike Smashville AND T&C if you don't like that format. I would be fine with T&C moving ahead of KJ64 but I don't believe it should.
I don't think Duck Hunt should be a starter... the stage is fair, but the dog screws up landings/punishments, the platforms are asymmetrical, etc... I think it's a great CP... not a starter.
Of the 3 "flying platform" stages (Delfino, Skyloft, Wuhu), I find Skyloft to be the most fair. I don't like water in general (changes the game completely) and Delfino can really screw you for landing in it. Skyloft doesn't really have that, imo. It has some walkoffs (both others do too) but the transforms are REALLY quick so it doesn't really matter. Wuhu is fine too, but the boat can kill you, etc so it's a spot below Delfino.
With the transformation between phases going quicker, I don't find a single reason to ban Castle Siege. yes the stage saves people from time to time (not like you can't just run and hit them again), but it's super fair and interesting in most matchups. I also don't see any reason to ban Halberd... it has the same issues and uses that it did in Brawl and that's fine, imo.
All of the yellow stages are in pretty random order. It's hard to say which of these is more or less fair. Imo, there are viable reasons to allow/ban all of these stages, so I think it has to come down to preference. The order I have them listed is probably the order that I would personally allow them in a tourney that I ran. I do still find PS2 disruptive. While it's fair, the wind or conveyor transforms pop up, and whatever you were doing, you have to change. It creates a 'worst case' scenario where you were dominating in neutral, wind up in the air when the wind transform starts.... and can't ever get down. Norfair I'm actually ok with, but it definitely promotes camping and leads to long games.
imo, all of the orange stages have obvious bannable issues, and they are going to be inevitably banned eventually whatever we do here. It sucks because I REALLY like the first 3 I have listed... I just don't think they should be allowed.
All the red stages should be unsurprising, considering my aforementioned bias against walkoffs. Seriously though, #legalizePyrosphere
EDIT: I also want to look into the Omega forms. Since they have some serious differences (grass traction, wall-jumpable walls, forms/cut-outs), I think it would be valuable to have a list of up to 5-6 legal Omegas that can be used instead of FD (maybe allowing opponent to ban walls, etc)
Minor update on 12/2 to change the order on some yellow/orange stages. Notable change is moving Mushroom Kingdom U to yellow... think we should probably revisit that some.