I don't know why everyone just defends the camera they own? I've owned the 5D Mark II, the 1Ds Mark III, the 7D, and own the 5D Mark III. The 5D Mark III beats the crap out of the 5D2 and 7D combined. It has way better AF than the 5D2, and has way better ISO performance than the 7D. It also can do auto ISO in manual mode. It has many more features. It's better than the two combined. If you can only take ONE shot at a time, and have a camera that's better than two cameras combined, how is this not the best choice?
If you are going for FF value, at a GREAT price and great IQ, then 5D Mark II's IQ is absolutely tremendous. I knew a lot of pros who didn't buy a 1Ds Mark III because of the superior ISO performance of the 5D Mark II. If you don't need the latest AF technology, it is a great camera.
If you want everything in one camera, I'd consider the 5D Mark III #2 on Canon's current camera list, behind the 1DX. If you don't need that and/or are worried about price, get the 5D Mark II.
I cannot recommend the 1Ds Mark III. Unless you only shoot ISO 50-400, outside, it's not going to be a good deal and you'll likely be disappointed. The only advantage is AF point spot metering. However, the files are pretty unusable above ISO 800. It was a great camera in its time, but has been outdated by technology.