From what I've personally seen, which by no means is totally the absolute last word on things, the Cobra bolt gets the best results. Cobra fits them to your breech specifically, so that less gas leaks and it doesn't wiggle at all, meaning more consistent and accurate shots with slightly better gas efficiency.
As to how much difference it makes, well, I've shot a few guns fitted with Cobra bolts and it does make a little bit of difference with it in. We chrono'd them with the standard bolt, shot some groups at short and long ranges, then put the Cobra bolt in, rechrono'd, then shot groups at the same target. The long range groups were tighter with the Cobra bolt, especially top to bottom, meaning the shots were of more consistent velocity. Is this worth going after? Well, among all the Angel mods that you can shell out money for, at least this does make some functional difference. I'd say at least give it a try.