Mixpanel is still fairly early in the game, but their development pace is pretty rapid. They also seem to be able to build on existing features pretty well; for

Mixpanel is still fairly early in the game, but their development pace is pretty rapid. They also seem to be able to build on existing features pretty well; for example, they rolled out the ability to build user profiles a few months ago, and then the ability to message those profiles a couple months later. I've used GA, KISSMetrics and now Mixpanel, and I've been personally been really happy with them. Nearly everything is there, and the missing parts look like they're being worked on.