500cc tops and power steering.
You can't put more than about 25hp to the ground weighing less than 1000lbs, and any more than that just costs you extra fuel.
Trail riding, mudding, etc; then more displacement/power is fine. For work - there's a reason Honda didn't make a bigger machine for a decade and still charged top dollar for it.
I like my 700 H1 Mud Pro from Arctic Cat, but I wish I had power steering and better fuel economy. The suspension bushings and brake pads wore out quickly for me, but I used to go floorboards deep in mud 2+ times a day, so it's not all their fault. Suspension bushings and motor mount bushings are weak points on the AC's. They're relatively cheap parts and not all that hard to replace, but they are known for being wear items.
I went to solid engine mounts, and urethane suspension bushings about 300 miles ago and haven't had any problems since.
Generally speaking, AC parts are reasonable, and they're easy to wrench on.