I've never had a problem with my Polaris starting in the winter. Generally about the second time it turns over it fires up. ('04 carb)
My dad has a '02 700 and his starts up fine as well, don't think they take any longer to warm up than any other quad I've ridden.
Lots of people make the mistake of thinking they have to have the biggest quad they can get (ME) at the time, but after you have one you soon realize a 500-600 will do just about anything you need it to do.
I personally don't care for the Grizzlies, I've ridden an older on extensively out in the Black Hills one weekend and a friend has the new 700 with power steering. Love the steering, but I think if you really played hard with it, it'd be a problem area eventually. I think they just feel too small though and twichy.
Haven't ridden the newer Artic Cats, but the older ones 4-8 years old I haven't cared for when I've ridden them. Love to try out the new Thundercat though...