Varies, but usually mish is the preferred position. I've seen ladies that absolutely REFUSE to offer this position. I've pretty much weeded them off my list, or only see them when virtually all other options have failed.
I really love to grind into a woman in this position. Nice and slow, feeling her thick thighs wrapped around me, face buried in her neck and just...FUCKING OWN her ass.
Spoon has become one of my really good favorites. The sensation is just INSANE, and it works well when the other positions have created too much soreness or cramping.
Doggy is great when it works. Some girls are really submissive here. The way they toot that ass up and just...let you DESTROY them. It's great WHEN IT WORKS. When doggy isn't working (i.e. bad angle, misalignment, too much height differential, etc)...it is THE WORST position. The worst.
Cowgirl works best with shorter chicks. When she's too tall it can be really awkward. RCG I'm really kinda iffy on it. When I'm rock hard, I point North, and reverse really goes against that grain. I'll endure it for a minute or two if the woman loves it, but in the meantime, too often I'm mentally counting down until when we can change positions.
On that note, I do like the raised up version of the RCG, where she's leaning back towards me. Ladies with great hip gyration are FUCKING AWESOME in this position.