What are some good stages to counter pick on a Pikachu and how can I effectively win.
Nowadays it probably doesn't matter. That mu can be won on the neutral stages(whatever they are now since we now play on 3 stages). But it all depends on how well you combat pikachu's Quick attack techs and how you make use of your jab game. If I remember correctly pikachu can get hit by jab to ftilt and I think jab to dsmash. Don't use down b as an approach or pika will block it and get you with one of his throw and follow up on it.
Just a tip that would work well with pikachu if he's approaching you at high %(90). Use fsmash tilted up, but walk the other direction and fsmash again and repeat. Walking away is done faster after fsmash tilted up because of the IASA(interruptible as soon as) frames which allow you do another action just quickly.
It's sad that I still remember anything about this game.