PSP is the best system this gen for me. It has the perfect mix of bite sized strategy, puzzle, platformer, and action gaming and it has slowly stolen just about ALL of ds' rpg support making it the true rpg king of this generation.
I love both systems, but it's clearly the 16 bit wars all over again:
SNES - emphasis on "immersion", rpgs, storytelling, epicness, realism.
Genesis - emphasis on pick up and play, action gaming, platformers, lacking in rpg count.
SNES = ds (adventure games, rpgs, occasional casual game)
Genesis = psp (puzzle, platformer, action, strategy games, though it has the rpg output that ds lacks making it even more well-rounded)
As someone who was clearly in the Genesis camp, psp wins.