To not just say "Use other thread blah," I'm going to actually respond.
There will ALWAYS be one stage that Pikachu should ban. Brinstar. Other than that, play on every stage that is legal in your region, or even the stage-list of nationals we are going to. Hell, I even play on Brinstar because it helps my training partners get better on it. Halberd is amazing for Pikachu. The low ceiling helps get earlier kills, and the long part when it lands is great for CGing. The platform is also good for wrap-around T-jolts.
Battlefield is good too. It is a basic stage but with platforms. The platforms can help Pikachu as long as we stay on the bottom/trying to time somebody out. QAC is amazing on them and, unless you get predictable, you can easily take a 30-60 seconds off the clock. Fairs/bairs are also good on platforms from under since it can push them off and either hit them or set up for a QAL or Jab lock (% dependent). If you are on the platforms...get off as fast as possible.
Yoshis isn't a good stage for Pikachu, but is isn't a bad stage either. THe slants make QAC more annoying, but it also helps CG a few characters that you couldn't normally (Like MK). However, the platform just kinda gets in the way of our aerial approaches (Like FF crossup fairs or FF bairs to shield poke) and it disrupts T-jolt camping to a big degree. So...dont' take anybody there, but you should still play on it to get the EXP. If you are only playing on your good stages you are basically setting yourself up to lose when it is your opponents turn to CP.