Well, basically all you need to know is that they will both prepare you for a real gunfight. End of story.
USPSA = FUN
IDPA = WTF?
C'mon folks!
Only one comment so far that is arguementative and nothing at all that is childish and futile.
My foundations are quivering.
Funny, I counted two that are childish and futile?!?! I hate this debate. Both disciplines are more alike than they are different.
I encourage you to try at least try both. Welcome to shooting sports!