Touch choice. If I were you i'd sit Avant. Phili has a tough matchup against the Titans and I don't see Phili really getting a passing game going. I think both Driver and Williams have bigger games than Avant. I don't think you need to worry about Gates and waiting to here the news about him, he will play (at least from what I've heard). At this point, the Chargers can't afford to sit and let Gates heal, there is a big difference between the Chargers going 2-5 and 3-4. If he has a chance to play, he will.
Mike Williams should have a big game against a bad Arizona defense, and now with Deion Branch gone, he is Hasselbacks #1 target. Driver should have a typical Donald Driver game. 50-75 yards and the possibility of a TD. Go with Williams and Driver. If you really want to play Avant because he plays the early game, then go with Avant and Williams.