Do you need portability? If not, the 21" iMac would probably suit your needs.
I recently upgraded from a 24" 2008 iMac that, although was still working fine, recently died with the anticipated repairs costing more than it was worth. I deliberated back and forth between the 27" iMac and the MBP with external monitor. The thing that convinced me to go with the MBP was the speed of the 512GB SSD compared to both the 1TB and 2TB Fusion drives, as well as the desire to unchain myself from my workstation. I've had it for 2-½ weeks, and really could not see going back to a desktop as my only computer.