I mean, that is a tough question to answer. If you want the screen real estate, go with the iMac. A top spec iMac will be faster than a base MBP. Also, if you are talking about updates, we have no idea what will be in the iMac next, so it is impossible to speculate. Right now the iMac has 2.8GHz processor, which usurps the MBP. You have a desktop now, if you feel you like how the setup is going, then get another iMac. If you have had many times where you wished for mobility, maybe it is time for a change. Also, maybe you keep the Imac and get a MBP?