Hi nine2five,
I used their threesome service a long time ago and all I can say is that it was worth every penny. The only problem now, I cannot tell you who would be a good combination. I believe I had Manami and Mako together back then but now Manami is independent and the remaining girls, other than Mako, I'm not so sure about. I heard in passing via another frequent user of AM that some of the girls didn't do girl-on-girl or actually get along very well. I checked around for other recent reviews, but there are none right now. Kumi is now gone, so I would have to go with Ai and Yumika. Both them are usually hot to trot and I don't think they would have any problem getting along in a threesome situation. Also, a word of note, the pictures on AM's website for threesome are way out of date, most notably, Manami is still pictured in a few of those advertising shots. Matter of fact, one of them is Manami and Mako together.
Oh Kumi, How I will miss thee.