For most applications a utility ATV would be most versatle. I'm most partial to Hondas, (all of our dirtbikes and quads are Hondas due to absolute dependability) but Yamaha makes pretty good ones as well.

Size is a serious thing to consider though. If you are of ample size and strength you can get a 4X4 quad up to 650 ccs very powerful and very capable with good load capacity and towing capability. If not, there are smaller ones to fit most anyone. My wife has a Honda Recon 250 2WD that is much more manageble to handle but still has plenty of power and even though its 2WD it goes pretty much anywhere you want to go in the Southwest. If you live in an area where there is a lot of mud a 4X4 should be consided. Either way if you buy one and intend to use it as an alternate bugout vehicle invest in a winch. A stuck quad is a bear to get out by hand. You can get a Warn winch for a quad for around $350. A small investment if you are putting your survival on the line.