They're both great machines but in order to answer your question you have to decide what you want it for. If mainly static you don't need portability it is undoubtedly the iMac that wins but if you need to lug it around the MBP is the daddy. However, MBP are extremely nice and I actually sold my iMac to get a MBP because I was moving between two locations. I sacrificed a very small performance hit for portability and have no regrets.
The bottom line is simple, if you need to move around with your computer MBP, if not iMac.