The Cliq is a more updated device.... it has the Google experience with the MotoBlur interface which is a hate it or love it type of thing.... luckily it's centered around widgets so if you don't want them then you can delete them.
The Cliq has a 5mp camera with editing capabilities (kinda like what the iPhone implemented) without downloading an app... better keyboard (my opinion), more RAM, and upgradeable.
The G1 one is good phone, it's rootable meaning that if you are the risky type, you can download many roms for it. It's been around the longest so there are accessories, cases, and mucho support, and a lot of the glitches are worked out however, because of the lack of the ram its no guarantee that it will be able to continue upgrading to the different OS's coming out for android.