I have a 13" MB Air and a 17" MB Pro (wish they'd bring that back - especially as a Retina display!). If you travel, or want to use it on the go, the Air is awesome. I'm not sure I'd want to do much serious editing on even a 15" display, retina or not. Budget permitting, get the Air and a 27" Thunderbolt Display to use with it at home. Max out the RAM, and for extra storage at home consider a Thunderbolt HDD.
I have the 15" Retina display MB Pro. I am using it for editing in the field and generally I am very happy with it. At home I have the 27" iMac. There are very few instances where I end up reediting images that have been through Lightroom on the MB Pro. The Retina display is excellent. The Air is lighter, but not that much more. The difference is less than my RRS BH-55 ball head ...
1DXII, 5DIV, 5DSR, 8-15/4L, 11-24/4L, 16-35/2.8L III, 24-70/28L II, 70-200/2.8L IS II, 100-400/4.5-5.6L IS II, 200-400/4L IS 1.4x, 17/3.5L TS-E, 24/4L TS-E, 35/1.4L II, 100/2.8L IS Macro, 300/2.8L IS II, 600/4L IS II, Zeiss: 15/2.8, 35/1.4, 55/1.4 Otus, 85/1.4 Otus, Profoto B1