I'd recommend Git Extensions, still, as a good compromise between porcelain and plumbing. The most useful commands are all at your fingertips, with deeper ones available if necessary. Visualization is best I've seen - clean graph display, easy to read, and _doesn't lie in complex cases like SourceTree does._

SourceTree tends to treat commits with multiple ancestry in a very weird way that has led to difficulty on multiple occasions, where people think changes 'went missing' because SourceTree decided the other ancestor wasn't important enough to show.