Domke Gripper for me. I just like the price and the classic look. It stays adjusted long enough to carry the camera sling style, as I have problems hanging more than a couple pounds directly on my neck.
I used an Opteka hand strap for a while and liked it, but the plastic base where it attaches to the tripod mount is a piece of shit. If there is another brand available with a sturdier build (preferably metal plate?) that stays in place once you screw it in and doesn't bend and wobble like crazy, I would seriously look into buying it, but I haven't found anything so far.