I've lived in Kansas, Arizona, Utah, California, and now Montana and I've ridden several models of Polaris machines in all these states, my current machine is a CanAm Outlander Max XT with the 650 motor.
The reasons I chose this machine were based on my experiences with a Ranger, a General, and an older Polaris 4-wheeler.
Obviously the Outlander is narrower and I can get in to the restricted trails with it.
The side by side machines are more comfortable to some degree but they are easier to handle in bad weather, not withstanding Kansas winds. One of the problems I've already had to solve was how to drive my Outlander in a blizzard without being blinded by the snow and ice. I solved that problem by using a face mask and goggles. As for a side by side being warmer, I'd say that this depends on the circumstances. If you have no doors then I don't think that they are any warmer, with doors it's warmer at first but without a cab heater it will slowly get just as cold as a 4-wheeler but without the wind chill.
A side by side is so large that it tends to get high centered in deep snow, the flat bottom of the machine presses the snow down and causes it to ice over, you end up being high centered on an ice pillar. The only way off that ice pillar is to dig all of the snow out from under the machine. A 4-wheeler can have the same problem but it's a smaller machine and it takes a lot less time to dig it out.
Another issue I have with the side by sides is that they have a far higher center of gravity and they will tip over easier than a 4-wheeler, if the side by side tips over you aren't going to tip it back upright by yourself and while it's difficult to do it to a 4-wheeler, it can still be done.
A 4-wheeler doesn't have the storage space of a side by side but you can overcome that problem with a small trailer or a snow sled, both of which are actually a better solution than the limited bed size of a side by side. Both machines can get more storage space by buying a larger trailer or sled but I can see what I'm towing better on a 4-wheeler so it's easier to check my load from time to time. The side by side's heavier weight would allow you to tow a larger load than the 4-wheeler.
Another advantage of a heavier side by side is that, if you have a winch, you can pull a heavier object but that can be overcome by anchoring either machine to some heavy object.
My Outlander is a 2-up style so I can have a second person on board with me.