Think the Honda TRX 700 is it's new biggest competator but its brand new so not much word on it. Other than that Scooter is right, the Outlaw 525 IRS is next in line, then probably the Predator/Outlaw 500, then DS650 or KFX 700.
I think the Outlaw 525 has couple little things to watch for
The Outlaw 500's I think are good all around
The Predator 500's are good after 05
The DS650 has no reverse and the early mods had a plaque of things that weren't good
The KFX700 is just heavy, belt driven, not great suspension machine that I think 04's were the only iffy year that had oiling problems if you wheeleid or something. Something like that.
The only thing better than the 700R is the 700GYTR which I think just added a couple accessories factory. My buddy did say out of the box they aren't that fast until you get them tuned. Also if you do any addon's the 700 has the best most complicated EFI box, but it does not have any intake or outlet sensors so it doesn't know when you do any of those kind of things so you Have to get it tuned. I read that guy pulled into his shop, threw on a aftermarket intake and the machine barely got itself out of the shop.
Other than that, the 450's are THE way to go if your after high speed coupled with very aggrestive trail. The 700 is better if you are doing that + low speed technical trails because it has the torque to lumbar along.
I'm picking up a Predator just because A. my buddy has a 700 so no fun having same quads and B. I don't like following the crowd. Everyone either is after a Raptor or a 450 of some sort. I'll toss myself in the middle for a common machine, except picking up the Cross Country Limited Edition 1 year only model just to fit my gotta be unique side