Personally I prefer doggy style, and all it's variants because I enjoy both the feeling of deep penetration and the loss of control associated with that position. I will usually push out to help in assisting with the initial entry, but after that I just focus on relaxing and enjoying the sensations.
As far as the second sphincter, I've been with a couple of guys who were able to hit it with their cock. As much as I love big cocks, it honestly hurt like hell, and the only thing I can compare it to is getting softly, but firmly hit in the balls.