I'm very happy with SmartGit, just as I was for years with SmartSVN.
It has all the features one can want. It's not, like some other Git clients, a simple shell over a standard commandline interface, but adds its own smartness on top of it.
I also like the fact that I can configure viewer and comparison tools to be used for particular file types. E.g, for my REALbasic project, I can assign Arbed as the viewer, and for other text files I use BBEdit.
Just like with SmartSVN, it's always been 100% reliable and stable for me. And the developers are responsive and helpful, usually within the same day.
If I had to complain about something, it'd be the user interface sometimes not following proper Apple guidelines. Sometimes a modal window doesn't appear like one (it appears like a doc window), and similar little things. Nothing of a problem, just a sad little result of this app being in Java, and Apple's Java support lacking (i.e. shame on Apple, not on the SmartGit developers here!).
Certainly give this tool a good trial run. It works well, is well maintained, and you can't beat the free personal license.