With the last 10.8.3 update the text even at 1920 x 1200 (15" rMBP, of course) becomes noticeably smoother and crisper at the same time. It was fuzzier prior to the update. I'm running mine @ 1920 exclusively. I've never even considered 1440 x 900 because as I did with my old MBP, I find at that scaling the desktop is pretty much unusable (for what I do).