The fact that all the tools can push to github make it easy to switch, which I just might do again. bzr was great, except for the fact that it just doesn't have that much traction...
I found bzr to be much as you described it - like hg, but slower. Nothing objectionable about the workflow (though the tools on Windows were very poor, I wasn't using Windows much at the time), just the perf on a particularly large chunk of code.