For me, to be a favourite duo, the girls have to seem excited to be with each other as well as with the male performer. Kissing each other is a must, swapping saliva and/or cum a huge bonus.
Absolutely agree. MFF titles with two girls that barely interact are just the worst in my opinion.
If the trailer just shows the obligatory "one girl looks up at the guy while next to the other girl blowing him" as the only indication of interplay I'm just going to peace out. I'd much rather just have solo works or MMFF two (partner swapping) duos if that's the case.
And yes, kissing is mandatory and messy snowballing is god tier!