We are having a lot of fun playing Street Kart, which is now in Pubic Beta. A lot of us have practically abandoned Gear.Club and Real Racing 3.
For those who have never tried SK, it is very hard at first, because the physics are realistic and karts handle much differently than cars. SK is a simulator, not an arcade game (such as GC and RR3). And there are a lot of elements to the game to learn, including, of course, the tracks. But have patience, go slowly, and it gets easier. Give it at least 2 weeks, and you will be addicted.
You can sign up for early access on the Street Kart website (http://www.streetkart.me).