The 13" for sure. I love the build quality, the solid feel, and the speed and performance capabilities. I also LOVE the fact that the 27" LED ACD now can be run down to the left side of the MBA and the cable doesn't have to split to go to power on one side and USB/sound on the other as the prior MBAs required. I haven't read that in a single review, and to me it's an incredibly simply yet pleasing change to the MBA. I don't use the extra USB, SD card, or anything on the right side of the MBA, and I don't like the holes in the side of the MBA especially the SD card slot.
I am very disappointed about the loss of backlit keyboard. Even though I type pretty fast and do well when typing, it's the location of the first key in the dark that ticks me off... and even though there are two bumps on keys to let your hands know where they should be, I don't type that way.
Other than that, I think the display on the 13" MBA is incredible. I love the 1440 x 900 resolution. I don't care for the display on the 11" MBA, and I really don't like the 16 x 9 aspect ratio on a display that small. It's just too small to be that short too.
I have tried to use both for typing, and I think the 11" would be great on a plane, but everywhere else the 13" is the clear winner in my eyes. I have written a full review of both, and am considering making some videos too... I am working on a new project that will finally be launched in a few weeks and will include the reviews. Anyone that wants my review can send me a PM and I will send them a link.
cheers everyone