I'll agree with free commissions or something like that for the same reasons everybody else has said: it's so reasonable and I know not everybody would have the cash to back-up some of the swag... that being said... swag is always nice.
Its totally great to get constructive feed back from another artist. Free artwork is the most common prize and it depends how good the artist is. You'll be able to do more than art though because you have lots of talent in different areas.
I love collectable stuff, even though I never really appreciate them enough to make them worth getting (they just sit on my desk and gather dust). I like plushies and figurines, little things that look cute/cool and don't waste my desk space. Not that my desk gets used for anything other than for junk storage. XD Swag FTW!
I'd say it depends on the awesomeness of the winning piece. I'd be swayed by free artwork or small commishes of fursuit stuff. I've been dying to commission someone to make a suit for me. Even if it was a fraction off a suit.
In other words, the choice of free art, or a discount on a suit or partial.