I have tried cocoonJS and phonegap side by side with my app and cocoonJS was much faster, however it was buggy so I went for phonegap. I didn't really notice a different speed between chrome and phonegap, but the lack of address bar at the top made the graphics much nicer with phonegap over viewing it in Chrome.

I can tell the browser used by Phonegap is not as good as Chrome. It doesn't popup the keyboard on text fields and things like that, which the Galaxy S2 don't do either.

I am hoping the bugs in Coocoon get fixed as that has the potential to be the best option.