Wow, I forgot to come back and answer this one...
I have 2 ways of answering this:
My favorite sex memory that I like to vividly recall is the first4-some I had. Beautiful day, bubbling jacuzzi, 2 sexy, fun girls, and my boy. Hot times, indeed.
The sex act I think about doing most often is laying face down on the bed, getting fucked from behind, with my favorite vibe on my clit. I love the double stimulation, and even better when I can cum from my clit with a cock inside me. I love to share that sensation of my pussy throbbing inside with delight.