MBA isn't a retina Mac though. Yosemite has graphical lag with retinas, because its drivers are poorly coded to handle all the superfluous transparency and blur.
Mavericks's iMessage works fine here, just like Yosemite's did. Last time I had issues with that app was when I was on ML.
iMessage between Macs on Mavericks always gave me errors. plus it was really slow on syncing stuff. Eh, i don't know. I could go back, but i don't really have time reinstalling everything. Again, it's not that bad on a 7 years old mac, i can't believe it frustrates people so much on 2013-14 macs.