I will be doing mild photo editing, the usual browsing, emailing, office sort of stuff.
I will also try to play Civ 5, or the newer game because those games are like crack
I like the idea of the air because it is so thin, but at this point the rMBP is pretty svelte as well and packs the power. The normal MBP really does nothing for me. It lacks the high end screen, but is still pretty bulky and is fairly expensive still.
Ultimately, getting the 13" base rMBP seems like a good 4-5 year investment and I think it is my best bet.