One on one, while I don't mind trying all sorts of positions, invariably, my favorite is missionary, occasionally with the ladies legs up on my shoulders for deeper penetration.  Not very exciting, but it's what I like.

If you want to talk about involving multiple people... Here are a few favs...

Guy laying on his back with 2 girls sitting, facing each other.  Once sitting on his dick and one sitting on his face.

A guy (or girl) fucking someone doggie style.  That person is getting fucked either by a guy, or a girl with a strap-on (depending on orientation or preference).  Optionally, add as many people as possible in a chain.  

And, of course, an old favorite party game... Tied down, spread eagled, and blindfolded, with no idea who is fucking, or sucking, or sitting on your face, or doing whatever.  Optionally, with a quiz afterwards on who did what and in what order

Water clones option 1 above is an all time fav for me. But at the Baccanalia event if I am fortunate enough to attend, I am looking forward to trying some variations on DP. Even a nice double BJ would be fun. I must say I like the erotic visuals offered by a group experience!

This site should give you and others a lot new of ideas ....

.....sort of a nifty animated Kama Sutra.