I'd get the MBA over either the MBP or x220. Thinness, SSD in all models, a UNIXish OS which actually runs some non-free software (and doesn't have people ask you what the hell is wrong with your computer), a crisp screen (the MBA has the same resolution as the 15" MBP) ... sorry, us MBA people are the most annoying Apple fanboys, right?

The only laptops I've seen which I've been at all envious of are later-model MBAs, and Toshiba's Satellite Z830 (damn that thing's light).

But if you don't mind a heavy laptop, the x220 does look nice. 15 hours video (with the $180 battery hump thing) definitely raises the bar.