I've owned the Canon 40D, 5DII, 5DIII, and I've used the T3i, 60D, 5Dc, and 6D quite a lot. I can say the 5DIII is by far the best of all these.
The 5Dc produces beautiful shots up to ISO800, the 40D was a work horse, and the 5DII was great, and the 6D is pretty much the same as the 5DII with a few extra goodies. But the 5DIII is pretty damn good at everything from video to sports to landscape to portraitsl the ergonomics are awesome, and it's built like a tank. It stands out above all in this category. The only better camera to the 5DIII is the 1Dx, but you got to pay and you have to carry a much bigger camera. Overall, I would ditch the 5Dc for either a 5DII, a 6D, or a 5DIII if you can cough up the cash. Then wait for the next generation.