Only Canon I'd avoid is the 50d – too many mega pixels crammed into the sensor creating too much noise – hence grainy pics)
Did wonder about that myself,but the 500D has the same pixel count and the 7D/550D has 18mp, both of those cameras get great reviews.
Surely Canon know better than to keep on increasing the pixel count and make cameras with poor image quality.
Admittedly I have a 40D with far fewer pixels,but had a 500D as a standby and never noticed a problem unless I went silly with the ISO
Not sure about any of this and would need convincing, I do know the 50D was much improved by turning off the noise reduction feature along with the highlights optimiser too