Garbage Counterpicks:
Corneria - promotes camping and wall infinites.
Green Greens - promotes camping and wall infinites.
Bridge of Eldin - promotes camping and projectile spamming and walk off kills.
Onett - promotes camping and wall infinites and walk off kills.
Hanenbow - promotes camping and projectile spamming.
When I say camping I mean that the stage is so segmented that the approaching player is extremely disadvantaged when having to chase/approach the character at that portion of the stage. Or in Bridge of Eldin's case there is just too much stage to run to, and the slower, losing character will never catch up.
I favor a generally loose counterpick list, but these stages just lower the integrity of the tournament. Most of these stages if they get picked will involve a stupid tactic and 8 minutes of unhappy players/viewers.
I have to disagree with a these for the most part. Those are fairly broad generalizations.
Corneria I can see. The wall allows for infinites, and it can be camped. I don't really think it's that easy to camp though. Especially with a ledge that can aid your approach at the top of the fin. Like Overswarm said, you either have to camp with your back to the wall, or close to the blast zone.
Green Greens isn't so bad for wall infinites. If you're fighting DDD or someone else with a wall infinite that won't break the blocks, break them yourself. I don't think you're that advantaged by camping the ledges either. You can always break the blocks then come in from the side if you feel it's too risky to go over the top.
Bridge is a little big. The fact that it's flat helps a lot though. If they're going to run the whole time they still have to get past you, and if you can't catch them doing so, I don't think it's as much a stage issue as it is a player being unable to get through a defense. It is risky crossing the gap for some characters, but it's not always there. If someone camps the edges they are at risk to get KO'd as much as you are, you just have to be careful of your approach. Walkoffs are going to occur mainly with Falco and Dedede chainthrows, both of which you have to have the opponent in between you and the edge, fairly close to the side and at low percent. Stay away or on the opposite side of them long enough to where you aren't at risk for a walkoff chain throw. Yoshi's Island is an issue because the edges are slanted and because of the smaller stage size it's easy to catch someone by the slope.
Onett you can't really wall "infinite" because of the cars. You can start an infinite, but it usually gets broken up pretty quick. Again, they have to be in between you and the edge for a walkoff kill, which is aided by the fact that there are walls.
Hanenbow doesn't really promote "camping" as much as it promotes a runaway game. And unless you are playing Sonic vs. Bowser or something that has a similar speed difference it isn't that difficult to catch up to them due to the fact that all the leaves are droppable ledges and you can move through them easily. You can run back and forth between the two trees or whatever the hell they are on both sides, but it's pretty easy to catch up to the opponent on either, and you can always pressure them into the middle as well.