Yawn, another thread, more misinformation.
All PS1 games should be fullscreen, or near enough (Depends on whether the game supports widescreen or not), and most play very nicely.
SNES is near perfect, unless its one of the odd cartridges with special chips, these vary from iffy to broken.
I've personally just got rid of a DS Lite, never got on with it really & all it ever got used for was Pokemon. The screen is better on the PSP, IMHO the games are much better, and generally I much prefer it.
Cheers
-Leezer-