Originally Posted by Stephen Probert
It's not the number of pixels that counts--its the quality of each pixel that does. The 50D has a much higher pixel density than the 5D, making it a great camera to shoot sports and wildlife with because of the additional cropability it offers. The 5D, however, beats the 50D in IQ across the board. Now if it's bells and whistles you're after, the 50D has got the 5D clearly beat in all aspects (Liveview, MA, hi res LCD, My Menu, etc etc) BUT if its IQ and ISO performance that you're after the 5D has it in the bag. For an older camera it performs just as well if not better, as in this case, than the latest offerings within the DSLR market when speaking of IQ. AF wise, the 5D falls a bit short IMO but only the outer AF points (center is very reliable and better in low light)...then again I have a couple 40D's that don't perform much better in this aspect and IIRC the 50D's AF is on par with the 40D. In the end, if you don't need the additional pixels or features and IQ is all you really care about go with the 5D. It's a phenominal camera. You may also want to seriously consider a 40D over the 50D as well...spend what you save on glass.
-Matt