I've been using Colemak for the past 10 years now and couldn't be happier with it. I have abandoned the German QWERTZ layout, mainly because writing code with QWERTZ is a real pain (curly braces, brackets and many other special chars can only be reached with the ALT modifier). Also, the layout for special characters on QWERTZ is different for Mac and Windows and I'm using both.
Colemak is way easier to learn than Dvorak if you come from QWERTY. With Colemak, all special chars and some common shortcuts (undo, cut, copy, paste) are on the same key as on QWERTY.
I don't know if I'm faster with Colemak than I would be with QWERTY now for normal text, but it certainly feels smoother and more natural, if that makes sense.
Unrelated to Colemak: I wrote a typing game a few years ago. It's more "playful" than Typeracer and targeted at beginners. I don't think it will improve your typing speed past a certain level, but it should still be fun: