I would say... not really tat important... but that is only me. I am using a 10 MP DSLR until recently and it served me well... if my old Canon hadn't die on me... I would have carry on using it. I would suggest that you read Rashkae's "What DSLR to buy" thread for better understanding on what to look out for when you wanted to buy a camera.
No one here can tell you what key factors and specification to look out for when you compare DSLR, because only yourself know what you want most. Different DSLR are good for different purposes... such as good movie mode, speed, high ISO, auto-focus in movie mode, vari-angle LCD, etc. So the best way is to go down to the shop, play with different DSLR and see which one feels better.
Other things to look out for is the expansion capability - such as accessories, lenses, etc. Buying a DSLR is not just a buying a camera... it is buying a whole system that include lenses, external flash, etc.