The 550D is very highly spec'ed. It main advantage is the APS-C sensor that will give better high ISO noise reduction.
The G10 will have an interesting interface, centered around the LiveView screen, but that would also mean that you shoot wrt to that screen rather than in a more traditional thru viewfinder method.
MHO, 550D for the potentially better image quality. Can't care too much about more things to 'interface'. But that is my preference and that differs from person to person.