this can vary from guy to guy, because as you probably know, different guys have different penises.
My girlfriend actually has a whole book on this. It outlines which positions are good to try if they guy has a small penis, or a freakishly large penis. Or if the guys penis is straight as an arrow or curves up towards the sky. For example if the guy has a small penis you want to avoid positions where the penis can easily slip out. And if the guy has a freakishly large penis you want to try and use positions where he can't over penetrate and hurt his partner. My girlfriend has her most intense orgasms during basic missionary position. This is because my penis curves upward so when we do it missionary (especially if we put a pillow under her butt to exagerate the angle a bit) my penis rubs right on her g spot, and at the same time she has both hands free to rub her clit while I'm fucking her. This is so far the only way that I've been able to actually make her "squirt". Of course we like to do it in many different positions, my favorite is a modified doggystyle that just makes her ass look sooo good. It's good to cycle through a few different positions as you have sex so you don't just use the same muscle group the whole time.
As for the "pumping thing. As you know, making love is not strictly physical, there's a very mental component involved, and not just for the girls. When a girl wraps her legs around my back, or claws my back a little, or rubs her tits in my face, it makes me feel wanted. That's a good feeling, and it heightens my sexual excitement. Unfortunately due to our anatomy, women are always going to have to be the "pretzely" ones.
Now if we're in a position where I control the action, I like to mix it up between pumping and grinding. The pumping stimulates the male and the grinding stimulates the female. I've been with some girls that I couldn't let get on top because all they would do is grind, and it would turn my dick into a wet noodle.
Guys aren't the only ones that can be bad in bed.