I usually go by the following rule:
Pick the stage you feel most comfortable on.
I can give you my general guidelines, but they are based on my play style and preferences.
- I hate Smashville because of the moving platform.
- I love stadium, and will play nearly any matchup on it.
- Dreamland is good only where the opponent can't recover or move as well as you. You can't get super good punishes on platforms, so I don't go there often.
- Fountain against characters who want to move a lot and kill off the top.
- Yoshi's (Melee) is really good against passive players, but I dislike it against aggressive players since I like spacing and dashdancing, and it's hard to do that there. Yoshi's is good if you're more aggressive than the opponent, or when they have amazing recovery since it tends to negate that a lot.
- Yoshis (Brawl) is a giant pain because the platform is too big for good punishes (unless you read the get up) and the sloped sides mean you really have to commit to the edgeguard
- Norfair should not be a legal stage, if it is, ban it.
- Green hill is fine, but don't pick it against characters who like to wall jump. The platform can be annoying, but also a surprisingly good recovery option. High ceiling helps against Fox, Lucas etc.
- Wario ware is weird, but I like it. The platforms are small enough that you can get good punishes, and the sides are short enough to negate most recovery differences. That said, walljumping characters can recover from anywhere is they don't hit the blastzone.
- Battlefield: I like it, but some people don't. Pure personal preference, depending on character and player you're fighting.
If you want more, consider the following:
- Who is the more aggressive player? The more aggressive player will often (not always) prefer smaller stages
- Who has the better recovery? If yours is better, go for larger blast zones, if not, go for smaller blastzones
- Is there a chaingrab / combo I can do that is interrupted by certain stages?
- How easy can I punish the opponent for making a mistake on a certain stage (dreamland is generally not so good for this)
- Who has the better kill options off each blastzone. For example, this is why I prefer fountain over Yoshi's for the Fox matchup, since it is harder to kill off the top there.
- How difficult is it to edgeguard? Stages like Wario's (multiple platforms), Smashville (moving platform), dreamland (multiple high(ish) platforms) may mean that you have to predict a recovery route which is bad for edgeguarding
- Did I notice any habits in game 1 which I can punish on certain stages? (e.g. he likes to dash dance, so smaller stages wont suit him, he recovers high, so I need a stage without high platforms).
- Any personal idiosyncrasies you may have (e.g. I like to dash-dance, so smaller stages don't suit me).
Alternatively, just go with your gut.
