Then I'd go for the iMac, but that's me.
You have to choose what's important for you.
i know technology advances, but i want machine that wont be outdated, compare the Retina Macbook with Regular Macbook Pro. Big difference.
if i want the iMac, im afraid an ever better model will release. Like retina display. im not that worried about processor because it know the ivy bridge wont always be the best. so a spec bump is okay, i wont want a re-design either.
i feel like the rMBP will be old soon, with another version coming up, maybe its going to have a re-design soon.