I'm a big MixPanel fan. We use it at my company. The big differences: a) More real-time. Nothing is 100% realtime quite yet but MixPanel is by far the best. b)

I'm a big MixPanel fan. We use it at my company. The big differences: a) More real-time. Nothing is 100% realtime quite yet but MixPanel is by far the best. b) Event driven - GA is pageviews driven, KissMetrics (also a fantastic product) is funnel driven. If you care about tracking key events and tagging those events with metadata that you can slice-and-dice later, MixPanel is the best solution. c) API - really great and simple API to get data in and get data out. This makes it easy to integrate MixPanel across multiple touchpoints (mobile app + web) for example, and have control over how you make those big piles of data interact/merge/display. Congrats on the funding guys!