(Good question!)
I think being told when my lover is fixing to climax is better because: 1. It's sexy to hear. 2. Knowing he's close, I can then maybe do little things to heighten his orgasm (clenching, verbal encouragments i.e. "dirty talk", a more intense touch/stroke/scratch/kiss...whatever) that might make him cum harder.
Being completely nude while having sex? Or, partially still dressed and going at it?