I did quite a few tests with different screen resolutions, as a super crisp look on all mobile devices was very important to us, we decided to go to the limit (especially on the iPhone4) and run the same resolution as the desktop version.
CocoonJS did pretty well! We have 7 parallax layers,particle fx, animations... and get 60Fps on most modern devices.
Here are the different game versions with their respective resolutions
Android:supports 1280x720 to 1280x800
iPhone:supports resolutions form 1280x720(iPhone5) to 1280x853(iphone4 &4s)
Facebook: same as Web and Web/Mobile
I hope that helps.