I ended up trying both and staying with the rMini. Yeah the colors on the Air are better than on the Mini and the extra screen real estate is definitely nice. But, after a year with the Mini's form factor, the full size iPad just felt awkwardly large in my hand (male with average sized hands). Typing on the keyboard is more awkward, and I found myself reaching more to navigate around the device. The Air is WAY lighter than the fourth gen iPad. But, it's not quite light enough that I want to use it one handed for more than a minute or two. Yes, I can do it. But it's awkward since the screen is so much larger and I definitely noticed my wrist getting tired. Two handed use is totally effortless and deserving of the "Air" moniker. But I really want a tablet that can be comfortably held in one hand. The Mini still fits that bill better than the Air, though the gap has narrowed considerably.
So, it's the rMini for me. But the specs of the two tablets are so similar that it really becomes a matter of personal preference. I don't think you can go wrong either way.