I like the Osprey Pixel I have because the laptop has a separate well-padded compartment at the back with a side zipper, which makes it really convenient to slide out (there's also a separate pocket inside that compartment for a tablet). However, it's not waterproof and it's a shade too large for British Airways' "personal item", so my 2nd choice is a Tom Bihn Synapse 19. That has no padding for a laptop, so I insert a Crumpler sleeve and slide the laptop into that.
wg