Gel. Thicker (like name implies) so it doens't run all over the place. Easier to work with. I am very happy with the stuff, both in ease of use as well as the improvements in accuracy in my rifle.

I used the Brownell's but they are probably the same stuff pretty much. To me it just looks like glorified 2-mix epoxy but the experts here might know what is better about it. I always thought there was fiberglass in the mix some how (thus 'glass'-bedding) but I don't know.

Like dcan said, make sure you use 2 coats of release on EVERYTHING you don't want the gel to stick too. I used masking tape (as per the directions) AND the release agent for most locations on the stock. Worked like a charm. If you miss a spot you might not ever get the action out of the stock again so triple check your work.