Gamboa. However, Donaire is probably a more "intelligent" fighter, and he utilizes a much more advanced style and approach. Donaire seems to still be a better "read and react" fighter, and he has been in with better, more live competition. So despite Gamboa having the better skills, per se, Donaire seems suited to go further, with more success and not as likely to get tagged and stopped or something. Gamboa also appears to be really full at his current weight, and with his frame, i don't know if he can go up in weight without adding unnecessary bulk.
Good thing for Gamboa is that he's starting more and more to implement timing into his game like donaire relies on.