At most two. I have a very good friend who unfortunately lives in another state but has said when we see each other, she wants my wife to pie her. She is absolutely gorgeous and I would love to see them have a full pie fight. I doubt they'd allow photos here, but it's not totally impossible.
I went for 2. Looking at the results so far, 2 is way ahead.
Is there something excessive or greedy about three or more? Or perhaps there's always the suspicion third girl will make off with your car or wallet while you're occupied with the other two?
Quality over quantity. I'm perfectly happy with one person if we're head over heels with each other. That said, I'm totally not opposed or don't have fantasies about multiples.
I've found out that I'm not a fuckboi though. I don't think I could just get with strangers though if it ever came down to it. I have to have some sort of relationship or friendship.
Until I can figure out how to grow a second dick, I will personally have to stick with one in my fantasies. Of course, I suppose since it IS a fantasy, then being as horny as a two-peckered goat might make the above a possibility? A bizarre and peculiar possibility, granted. But anything's possible when left to the imagination, I suppose.
So yeah; one it is. Preferably a very attractive one, and starting out as feminine and formally dressed up as possible. And hell; if it's going to be an actual fantasy- might as well even have her actually LIKE me in the process!
Way way back . . . before messy videos were shot . . . I could only fantasize about one, trying to imagine her mind, why she wanted to play in the mud, how she was enjoying it, etc. So my wam fantasies were built around one girl enjoying the mud and often included myself happening upon her and being talked into joining in.
But since wam videos came about, I've leaned more towards two, often with each of them focused on the other, whether or not lesbian activity took place. There would always have to be a lot of sensuality though, rubbing, smearing, etc. whether it was just one or two.
But three or more distills things too much. I can't focus on what any one girl is feeling or might be thinking. I enjoy the visual, but your question said 'fantasy' and that element fades out with more than two girls, simply because it's hard enough to imagine what one girl is feeling in the situation, then two is a challenge, but three is too difficult. The fantasy of what is going on in the girls mind is part of the thrill for me.
If it's a submerge-to-resurface-to-submerge video (Kym, Kristine, and Lena leap to mind), then two is the optimal choice. One lady can see what the other had done, then she preps herself to go under.