I'm not really sure - I think it kind of depends on the couple ie the postion that suits a tall/short couple may not be the position that suits a couple that are both the same hieght. The missionary position might be good because you're face to face so it facilitates communication. If you're on top you will be more in control so you can keep things at a depth, angle, pace etc that suits you you.
Maybe one of those sex books like The Joy of Sex might be usefull.
If you ask for access to the AO section the girls who post in there might be able to help you.