Whnever I can upgrade only one way, it is on the westbound leg. I don't sleep well on a plane regardless, but even in the winter, I find the daytime westbound leg to be hot (that sun seems to come through the windows right on me, and too long (with the tailwinds, the westbound flights fighting them, it usually is a longer flight on the return.

Also, I usually excited enough on my way over that I don't notice how uncomfortable I am until 3/4 of the way over.

Larry