My experiences with Hondas, Suzukis and Arctic Cats have all been good...they are very reliable machines. Not a fan of older Polaris models that were assembled with rivets, never ridden a Kawasaki so I have no opinion, and my buddy's Yamaha has been fairly trouble free.
For reliability, go with a mid-size to larger (400cc or more) engine, and if you plan on ever going with oversize tires then buy the biggest engine you can as the smaller engines will have a harder time turning them over in muddy conditions.
If you can find a model with power steering and fuel injection those are a plus, and worthy of the extra expense...ESPECIALLY if you go on trips with different altitudes where fuel injection eliminates the need for rejetting a carb for different altitudes. Power steering is awesome in the rough and bumpy terrain and acts as a shock dampener when you hit the rough stuff. Solid rear axle versus independent rear suspension (IRS) used to be an issue but I think most flagship models have IRS for a smoother ride.
Used to be a Honda man back in the day but their insistence on sticking with drum brakes on their new models (back then) made me switch to Suzuki so that I could get disc brakes on front and rear. Had a Vinson 500 5-speed that was a beast. Finally, bought an Arctic Cat 650 TRV so I could take the girlfriend along on my trips to Utah's Paiute Trail. VERY reliable machine, even with bigger tires and a carb rejet and performance exhaust.
My 1995 Honda 300 Fourtrax is at a buddy's deer lease needing some TLC, my hot-rodded 2003 Suzuki Vinson is now another buddy's ride (traded it for a Kia car for my daughter), and my 2005 Arctic Cat is sitting waiting for the next adventure
I don't know what an XMR is, but I'd avoid a chinese-made ATV altogether (if that's what it is) as I don't think they have good service/parts networks, whereas most major brands like Honda, Suzuki, Arctic Cat, Kawasaki, Yamaha, Can-Am (Bombardier) have service and staff and parts to fix what breaks.
Hope this helps and good luck