They are about the same price ($100 difference, iMac $1699, Macbook Pro $1799), and

iMac: Quad Core i5 2.7GHz  

Macbook Pro: Quad Core i7 2.0GHz

How can you tell which processor is faster?

(the iMac shows 4 processors in the Activity Monitor, while the Macbook Pro shows 8 processors)