If you have any mud in your trails I would avoid the Kubota. The RTV 500 I had did great the first several months I owned it but then the drought ended, we didn't have crazy mud but some soft areas...I spent most of my time winching it out. Then I figured it was my worksite tires so I purchased the Kubota "atv" tires and rims to give it another go....they weren't any better. Between the 3wd, very low ground clearance, weight and the hydro transmissions slow response the machine sucks in mud. A lot of guys will tell you how great they go in all conditions but mine sure didn't, Berretaman92 (??) purchased a 500 and put tracks on it...that one looked impressive because the tracks lifted it up several inches and he gained a ton of footprint but tracks are another over 1/2 the purchase price of the machine and make trailer a pain as well as slow you down even further.
Of the choices listed I would go with the Polaris 570 it's a great size and has good power as well as true 4wd. It will do both work and play, don't believe guys when they say you need a hydro to do any work. My Gator 825i is belt drive and is an animal pulling, hauling wood and plowing snow...the Boss V plow on it weighs over 400 lbs and hangs way out the front, I also put 600 lbs of ballast in the bed and my Gator doesn't notice any of it. Hauling firewood I filled the dump bed and then strapped two 40' x 10" logs to the back and proceeded to pull them through the trails to get them to the wood pile. I never wanted for more power, never slipped my belt and never came close to getting stuck....CVT transmissions work and that is why most every manufacturer is using them. The 825i is a great machine but it is very expensive...because the dealer is very close it was worth the cost to me but it really is very expensive. I am impressed that JD offers the extended warranty on their machine for an extra 2 yrs though...it shows they have good confidence in their product, I see a lot of Gators on the trail up here now because they can hang with the sport utvs....I've only seen 1 RTV in the woods ever up here and he was going extremely slow because the ride was hammering him on the rocky stuff.