Esna will happily admit he prefers capsuleers because they offer a better, more challenging fight. That said, the only faction he really wants to shoot at is Blood Raiders, and there's a decided lack of Blooder capsuleers to pew.
The others he just shoots because A, they fire first, or B, he has reason to believe they will/are endanger(ing) someone or something he cares about. Beyond that, they can go do their own thing. This goes for both capsuleers and NPCs, although with the other capsuleers there's also a third factor - they're willing, he's wiling, let's go.