iMac. You'll get a much better machine for the same price, and in the future you still have the option of using the iMac as a display for another machine (Target Display Mode).
This, my friend, is the seemingly eternal question we are all asking ourselves in this very forum. Unfortunately the answer you seek is one of inconclusiveness. I would tell you to wait if you can, but then again I have no idea when that wait will end. If you are in desperate need of a machine to sustain your livelihood then definitely buy now, else join the ranks of the despondent and keep reloading the Apple store page.