well imho it depends on what u wanna work with..
do u use midi only? do u use audio? (i.e. wav-samples)
should it support asio drivers? wmd? gsif??
how much do you want to spend??
there's lots of possibilities, and there is no BEST soundcard, so that's always a very difficult question
edit: also this should have been posted in the "soundcards" forum ;)