It's really hard to tell because Uber's released data is kind of sketchy [1] and there isn't good aggregate data for the taxi market. You can look at individual stories like [2], though. Anecdotally, if you want to do it full-time, taxis used to pay significantly more, mostly due to tips, lower maintenance costs, and more efficient rides. Competition from Uber and Lyft have depressed taxi income recently, though, so it's no longer clear which is objectively better.

[1] http://www.huffingtonpost.com/2015/01/22/uber-drivers-pay-st... [2] https://skift.com/2015/08/03/taxis-vs-uber-in-nyc-according-...