the doo's are nice, but it's really a preferance thing, what kind of riding do you do? like, ditchbanging needs a ditchbanger (REV or Viper) lots of trail stuff @ high speed needs a fast, powerfull sled (Mach, SRX, RX-1) it's totally in how you ride, I would recommend going out and giving them all a "test crack", see what they feel like to ride. I've been riding yamaha forever 'cause my uncle has a dealership, but I don't mind the bombi's at all, there nice sleds, and if I was gonna get anything other than a yamaha, it'd be a mach for sure.
as for the vipers, ya, Sled dog's got it right on, they a really weird sled, like, I've ridden 2 (a buddies, and my uncle's demo) and they feel weird, but are seriosly modifiable, like, my budies (on the race team) was stock when I rode her, and she hauled ass to 140kph, then that was it (that's something like, 90-95mph) and I was really disappointed 'cause I'd ridden an SRX last year, and it hauled hard till the speedo was buried and then some (we radared a stock one at 139mph).
the SECOND time I rode a viper, it was my uncles which he has set up, and the very first thing I did was find a long field that I've been riding forever, I set her up at the fencepost, and just took it like a drag race (I grass drag in the summer) U know the routine sled dog, lean way forward, then pin the hrottle, stifen up the legs and throw yer ass to the back of the sled till U can feel the taillight under yer rump. ANYWAYS, when I pinned it the ski's stood RIGHT up (like, 4 feet off the ground), and before long the speedo was at 199 kph, and it had been hauling hard up to that, so I let off after it stops rising and wonder why it capped like that (couldn't feel it stop pulling) then I realized, the first digit in the speedo is only a 1, so at 199 it's buried. so I was pretty impressed, but it still wasn't an SRX, so I took it down a drifted in fence line that seriosly resembled a part of a snoX track, and this is one of those things that the SRX just wouldn't do, but my god, that viper flies like a dream over the drifts, easy to control your attitude w/ the throttle and break so that U land nice and gentle.
anyways, so ya, vipers are nice for ditchbangin, but they're not straight line rockets, same goes for rev's I would expect. but seriosly, take them for a test drive before you go out and buy either.
they may be called snowmobiles, but hiding behind that is a cheap excuse to not grass drag.