Zieman makes some really nice side load ATV trailers.
If you want something that will double as a snowmobile trailer, though, you are probably going to have a split tilt bed trailer. I've used a snowmobile trailer to haul quads. Other than having to hit it at exactly the right speed to get the bed to flip flat w/o sliding back down, it worked OK.
Many snow mobile trailers have the little tiny tires, though, and I'd want 15" wheels or bigger.