To answer the actual question - screen size alone is not a huge feature to me any more. If it otherwise ticks all the boxes, I might be tempted to return to a 17 or 18 again, but that would depend a lot on the specifics - I'm not going to order a hypoethtical 17" ridiculously thin Air over a 16" high end pro, just because it has a bigger screen.
(Also, why is there no "maybe, it depends" option on the poll?)