I use everything from willow branches tied together to a big heavy sturdy Primos Tripod. It all depends on where/how I'm hunting. From a blind, I use my heavy Primos tripod, for my guns that don't have a proper sling stud, I use a Cabela's adjustable bipod (normally attached to my pack with the cradle up so I can quickly take off my pack, sit, rest my rifle and shoot from the pack, I've actually shot a few deer that way) and for everything else, I have an adjustable Caldwell's bipod attached to my rifle. The Caldwell bipod (I forget the length), is for kneeling or sitting, if I'm shooting prone it's in the open prairie and the critter is far enough so I'm using my pack as a rest.
On the not so odd occasion that I forget to pack a bipod, or forget it in the truck..., I make one on the spot. In this case, I always cut branches longer than I need and adjust down to adequate length.