Mix & match, mostly depends on what turns him on best. If he's truly huge, I like to go doggy first or sometimes me riding on top. Once I'm accustomed to his size I really prefer him to be pushing against a solid structure, like the floor. On my stomach at the corner of the bed, one leg on each side, is a lot of fun.
When he's getting close to cumming I really love to be at the edge of the bed on my back, eyes-locked with him pressing my legs against my chest as he plows like a draft horse. Doing the same on the floor (a thick rug is preferred) is incredible, too. Sometimes it feels like he gets an extra inch or two like that!