I think that the CPU on Pokemon Stadium 1 and 2 were awesome. The cpu on the gameboy is so terrible. At least the Stadium games had the opponents use strategy like the Toxic, Double team, Protect, Fly combo and the defensecurl/rollout combo and the curse/extremespeed combo and the swagger/spych up combo. You never see anything like that in the gameboy games.
I was lucky enough to beat the master ball challenge cup on my first try. I found the ultra ball one harder. I kept ending up with crappy Pokemon lke Charmeleon and Noctowl when the opponent would have Magneton, Quagsire, Muk, Dragonair, pupitar, Vileplume, etc.