I never know what attracts guys in the duo situations.  Do you like to see two girls of the same age/look or do you desire a contrast?  Do you like to see ladies with similar personalities and providing styles or different ways to mix it more? Do you desire that they are both truly bi-sexual or do you prefer the "gay for pay" where the focus is more on you and not all three equally? 
Now I'll be honest I am a girl slut, if you look at my reviews I think I may have just played with more providers than many of you guys lol.  I am genuinely bi-sexual and I love the change up of from the traditional 

 So when I meet a new lady I really do get overly excited about what kind of fun will go on with another provider in the room!