The question is, are you going to be using your GUI in addition to or instead of the command line. GitX fits into my thinking as a supplement to the command line (I'd never create a repository or commit with it, I just look at the graph and changes), while Gitbox could be a replacement for using the command line on OS X... I just think it needs a graph like GitX (and every other git GUI tool) and it needs to act a little more like Versions.app, which gives the impression that it's not just a few simple tasks for repositories, but the all-in-one experience.