Its hard to pick one, because they are all awesome in their own way. The visual of going in from behind (doggie and standing doggie) is amazing, but I usually cant finish that way. Missionary and facing her is great because I can see her face and possibly kiss her during such an intimate act. Spooning is nice because our entire bodies are in contact from head to toe. Her on top is incredible because she is moving and grinding in the way she wants to feel good while I'm inside her most intimate hole.
But you left out my favorite, which is her lying on her stomach, with maybe a pillow under her hips while I lay on top of her. Most of our bodies are in contact, entry is easy, she can arch her back/hips and thrust back at me, I have my arm locked around her neck (we play some D/S), and I can whisper in her ear and bite her shoulder as I 'take' her ass! Yum yum!