I think we have five or six different ones. I started with one which I think is made by Trident. It's fairly broad, and the inflator is only for oral inflation, and requires that you push on it with your teeth to get air in. It was a PITA in cold water.
After using my buddy's, I bought the Halcyon 3' bag. It has a nice inflator which will work with LP hoses as well as orally, and I could get air in it with cold lips. It has a standard dump valve as well. I liked it a lot.
Peter bought the Zeagle bag, but it's bigger and requires more air, and has one of those oral inflation valves you have to push on. I didn't like it.
I'm currently carrying Tobin's SMB. It's a 3' bag, with a tapered shape, and it's delightful how little air you have to put in it to have it full and visible on the surface. The inflator is oral, but you don't have to do anything fancy to it to get air in it, and it's big and round and easy to get cold lips around. The dump is a flexible slit in a round soft plastic window, and I'm still ambivalent about it, but it does work, and it certainly works well as an overpressure valve. At any rate, this is my current favorite.