Here’s a comparison of pros and cons of the Canon 50D and Nikon’s APS-C (DX crop) camera which was introduced around the same time, the Nikon D90.
Canon EOS 50D Advantages
Resolution: The Canon 50D has 15 MP (megapixels) of resolution, while the Nikon D90 only has 12 MP. If you shoot low ISO and have a requirement for more megapixels to help you print really large, or if you have a need to crop a lot, the 50D is the camera for you.
Nikon D90 Advantages
In-camera CA (chromatic aberration) correction: Andy Westlake, a DPReview.com reviewer, has this to say in response to a question on the excessive CA in this Canon 50D photo, and about the comparisons between the sample photos posted from both cameras:
Canons don’t have in-camera CA correction, this is only available when shooting RAW and processing in DPP (and then only for profiled Canon lenses). The 50D does however have vignetting correction built in.This in fact is one area where Nikon are well ahead; the D90 has auto CA correction on all lenses, vignetting correction, and even adds distortion correction (profiled for known Nikon lenses) in the retouch menu.
Auto CA correction has a significant impact, as it also improves overall IQ towards the corners substantially, and is probably one of the main reasons the D90’s JPEGs look so good.
Spot metering linked to AF point: All Nikon digital SLR cameras have this feature built-in, and the D90 is no exception. With the camera in spot metering mode, the currently-active AF point is the spot meter, while on the Canon 50D, the spot meter is always at the center AF point only.
Record 720p video: The D90’s movie mode doesn’t produce clips that can rival HD camcorders in terms of sharpness and sound quality, but I’ve found it to be immensely useful to record events as they happen, and when I don’t have my camcorder with me.