While I prefer walking, we have and use 2 different sized quads and a Commander side by side (my bush Porsche as I call it
.
If I had to have only one, I would say go for a 400cc quad.
Light weight, gets the job done, and cost effective.
Lighter weight tends to leave the least amount of wear on the ground (obviously depends on your tires...but you get my meaning) which keeps in line with not leaving a scar behind in the wilderness.
Even on our own land I like to keep things as unmarked as possible.
A quad also allows you to jump off faster (compared to a sideXside) when I'm riding our fields or bush trails and I need to shoot at something.