I have wondered the same thing for quite some time now and I decided to simply install Ubuntu on my 2013 Macbook Air. Everything works out of the box (except the iSight webcam), and with a bit more polishing, you get good battery life and trackpad gestures.

Before taking that decision, I had read plenty of reviews of various models, but could not find a decent PC out there that would be both light, and powerful, with a good screen (something the MBA might not be best at to be honest). The best results I found were the Yoga 2 Pro (but Linux compatibility does not look great), and the Asus NX500 that has not yet been released, and that appeared to be disappointing based on pre-production version reviews.