Too broad of a question to answer honestly. Without going into great detail, I've got a good bit of experience with many of them and am around people with a ton of experience. However I have been out of the "latest and greatest" game for quite some time now and don't even look at the new models when they come out(because I get googly eyed and that little voice starts telling me how bad I need them).
I'm very partial to the tweener size UTVs(Polaris General, Can-Am Commander size) personally that can really do it all. Still fit down the ATV trail at deer camp, can do all the work-related stuff, etc. Smaller than a Ranger, bigger than a Rzr.
I have no seat time on the newer Yamahas, but have heard they persist in being a little underpowered just like the ones that came before them. Not that millions didn't have great success on a Rhino, but I wouldn't want to spend that amount of money with any doubt in the back of my mind in that regard. Have a little bit of seat time on a Pioneer. Really like them and I'm sure Honda will eventually sell a ton of them. Ton of seat time on a Commander/Maverick, none in a Defender. 5 years ago they were built a whole lot better than everything else, without question. More expensive but worth it. Now others seems to have caught up to the little things they were doing right(5 layer waterproofing in plugs, thicker wires in the harness, frame clips for all of the connectors, very inventive designs to make easy to work on). Ton of time on a Ranger, which is hit or miss, depending on which exact model and who is responsible for taking care of it. Lot of small(wiring harness, suspension bushing) issues, but easy to work on. My favorite right now is a General, which I recently set up for a buddy and got a good bit of seat time in. Seems to be very well-built, well-designed, and thought out. Just the right size. These things have gotten a lot closer to perfect out of the box now. And it's got enough power to give you a real rush. Surprised me even though I was expecting it. My biggest advice is to stay away from the Kawasakis at all cost.
The big thing is "what goes wrong with them over time -- and can I get the parts locally and fix them myself". Lot of Rangers out there now with 5000+ miles on them and basic wear items on round two or three -- and you can go buy every one of those items at Got Gear this afternoon.