I personally recommend Un-natural Sex 9 with a great cast list, Gauge does double anal in the first scene and is followed up by the likes Melanie Jagger and Rita Fitalayno (sorry if its spelt wrong), that was one hot film!!
I think that 15 was great too but only seen it onece so cant tell you who was in it...
I've got numbers 12 and 19. 12 is definitely worth getting if you're a Taylor Rain fan as it's the only scene she ever did double anal in. 19 is also awesome for double anal as it features Tory Lany and Cindy Crawford both doing their first double A scene. Plus Velicity Von gets DP'd as well.
I love this series and its my favorite from Diabolic. My fave volume is #4 which features Monica Sweetheart, Daniella Rush, and Sophie Evans among others in scorching anal action - all wonderfully captured by the late Jon Dough. Highly recommended!
Volume 10 is another particular fave of mine, mainly cuz it features Jayna Oso in some very nasty double anal action as well as hilarious interview footage. Chico Wang took over the series starting with this title and he does a pretty good job at the helm but he does take it in a bizarre new direction.
I personally would suggest the titles in which Everhard performs. I simply do not have the male talent to perform at a level in which Everhard does. Therefore, there came a point in which I had to try to redefine the title by throwing in more double anal, convincing new girls to try double anal, and adding a sort of more perverse element in the scheme.
Personally I would suggest #8 and #9. They are vicious to say the least and I say that as the director who has shot more gay ass double anals than any director out there in the past 3 years.
Un-Natural Sex #6 is a classic with Miko Lee and Cherrie. Cherrie takes one of the best creampie shots of all time and Miko Lee gets absolutely cum-drenched in the likes that I've never seen before.
"Two Shades above the rest", - The Secluded Paradyme.