We have a Kubota RTV at work and it's a very strong machine, build quality is good and the engines are known for being trustworthy. It's got a large payload capacity and pulls small trailers off road fairly well.
On steep ground it's best to stick to straight up and down as rtv's do feel a little top heavy compared to quads. It would be my choice of machines, maybe with a set of doors as when it's blowing with rain it feels like you get wetter than being stood outside!
There's also a couple of quads, Honda of course! They are powerfully for the size but a little uncomfortable with a passenger, tools, feed and the dog loaded on.
We've had a a couple of John Deere gators and we didn't rate them really, they were expensive to buy initially expensive when they went wrong and didn't want to take much in the way of a load especially on hills.
The best advice when buying a machine is to really look at what you need and buy the best you can afford and make sure you factor in servicing, look after your machine and it will look after you.