I use a Seat of the Pants harness that I've had for 8 or 9 years. There are a bunch of good harnesses on the market. I'd look for one that can be converted to a lumberjack-style belt that will allow you to run your strap around the tree and connect to both sides of your waist. This is ideal for hanging stands and allows you to comfortably lean back and have both hands free while hanging.
The only problem I have with the Seat of the Pants harness is that the strap that connects to the harness isn't very long. I like to use a cinch rope from Summit to give me a little extra room. The rope attaches to the tree, and you connect to a sliding cinch knot. You can tie a knot anywhere along that rope to control the distance of your fall.
Either way, get something that will leave you in an upright position should you take a spill. It's also a good idea to keep an extra screw-in tree step on your person. If you hunt out of a climber, that screw-in step can help you get back in your stand. The Seat of the Pants harness has waist pouch in the small of the back, and I keep the step in there.