I wrote a while back in 2012 about Uber and its competitors. Read it here.
Recently, I used MyTaxi. It's huge in Germany. I am really not a fan of the app because it doesn't work for me. It's extremely buggy and difficult to use. When I press book, nothing happens and no error message is shown.
My guess is it couldn't save my phone number correctly so my orders weren't working. I managed to book something using the web version on mobile but the driver didn't show up or left without calling me. So that's more than 30 minutes of frustration in the rain.
On my second try that day using the web version (because I really needed a taxi), the taxi showed up but the driver required that I pay in cash and charged me extra for luggage. I couldn't even use the promo voucher too. All in all, I had pretty bad experience and the app is still unusable for me. Customer service is responsive but was no help and just asked me to create a new account. No compenstation was offered as well.
That said, it's fleet is much better than Uber in Berlin and affordable. You can use cash to pay which might be a plus for some folks.
If you want to try it, here's a 10 Euro promo code or gutschein, just enter "TaigeZ1" after sign up. Good luck. My colleague had a seamless experience and likes the service a lot, so I guess it's down to the company's technical problems.