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I'll agree with and summarize the gist of this thread so far. Any of the cameras mentioned take great photos but to get the best image quality for general photography, get the most recent 5D you can afford. Crop cameras are a compromise to keep cost down and performance (i.e. frame rate, reach) up. Since I got my 5Dc I've used my crop cameras almost exclusively to increase the reach of my 100-400 since the 500 and 600 mm lenses are beyond my budget (and weight carrying capacity ). Unless I need reach, I reach for a 5D.
The 7D is a fine camera (especially if you're shooting things that move), but its image quality is not quite up to the 5D2. That doesn't mean, by any stretch, that it's bad (just look at Imagemaster's photos), but in less expert hands (mine) I can tell a subtle difference (pre-processing) in the quality of the images between the 5D2 and the 7D
I shoot raw and post process so I'll go beyond StarNut here and say that 5D images are just easier to process and 7D images (more so than my 40D) require a lot of post processing to get their best. There have been many threads devoted to this subject. But, even if I carefully PP a 7D image and reduce it to 5Dc resolution, the 5D image will usually look slightly sharper and cleaner with less shadow noise. The 5D2 images are just as clean and easy to work with as 5Dc's, but give you more resolution to work with. If you shoot JPEGs, this PP effort difference is irrelevant and the IQ differences may be subtle as StarNut says.