Wanted to start the same topic some time ago as well
First of all, my favorite scenes are with two or three girls (and 1 to 8 men...), but if I don't like one of the girls I probably won't buy the scene.
So nice pairing is important for LP to sell scenes and for us (or at least for me) not to be frustrated that I have to pass for a scene with a model I really like, because she's paired wit a girl I don't like. In general I think the best pairings are with girls with the same body type and especially the same length. A small slim girl combined with a big tall girl for example is a no go in my opinion. My favorite models are the slim russian and eastern european girls, which are luckily the main type of models on LP. But for the ones who like girls with big butts... I don't mind if LP shoot scenes with them as well, I just recommend not to combine the two different body types (only exception I would make for athletic girls like Kitana Lure, Laura Crystal, and Billie Star; they can be paired with all girls actually).
That said, here are my favorite combinations:
Karina Grand and Susan Ayn
Lindsey Olsen and Ariadna
Linda Sweet and Nataly Gold
Blanche Bradburry and Nikita Belucci
Kitana Lure and Laura Crystal
Lita Phoenix and Goldie
Leona Levi and Susie Q
Anita Bellini & Timea Bella
Arwen Gold & Helen Star
...
Of course the list can be endless... but I'll stop here