During a threesome with my buddy and his wife I always enjoyed eating her pussy while she sucked my cock and her husband would fuck her pussy and my mouth, going back and forth from her pussy to my mouth. She was a trooper giving each of us equal time in her pussy and each other's mouths.
I am a big fan of inserting a wife as she and her husband enjoy the 69 position. But I think my favorite maybe her in reverse cowgirl and me pushing his head tongue out into her ass.