We've now tried it both ways, first rear-facing NRT-BKK UD 744, and forward-facing a few days ago on a 767 LHR-ORD.

Despite our somewhat queasy stomachs, we didn't experience any mal de air and actually felt more comfortable sleeping in the rear-facing seats with our heads slightly raised.

Second, take-offs and landings rear-facing provide a fresh view. Other than that, we didn't really notice any difference.

On our flight last week the FA was trying to relocate somebody who desperately did not want to sit rear-facing but eventually settled down.

Cheers,
Fredd