Shouldn't the xxD series of Canon be compared to Dxxx series of Nikon? (i.e Canon 50D or Nikon D300)
Generally, mid weight series of the two brands features Magnesium Alloy for a more rugged and heavy-duty body. There're of course differences in features too which at the end of the day boils down to your needs and there isn't any better recommendation than the suggestion of trying them out.
For budget shooter, I think it's good to go for D90. As the kit Lens is 18-105 VR.
So it actually covers a pretty good range. Maybe just add a 50mm prime lens for portrait shots.
So pricewise is quite affordable too.
Whereas for 50D, if you take the 18-55 kit. The range is actually pretty short.
If you take the 17-85, many said the image sharper & clarity not good.
So it depends a lot on your budget & which system feels more comfortable in your hands.
Happy shooting when you made up ur mind.
if you do not need HD Video, Better Live View and other minute improvements, can consider the cheaper 40D or even a 2nd hand 30D. Use leftover money for good glass and some photography lessons, you are set.