Not caught up on HxH, but spoilers:end of spoilers
I do not believe Hisoka was ever really "with" the Phantom Troupe. He basically killed one when they were in a non-active time period, took their spot for the York New events, and only bothered with the Troupe when there were interesting jobs/fights available. Otherwise Hisoka just peels the identification tattoo off and is a "normal" Hunter again. My understanding of Hisoka's motiviations boils down to: Are you strong? Are you likely to become stronger? If no to both, he does not care about you and has no issues with killing you. If no and yes, then you get the situation with Killua and Gon. Interested, and will attack if he has to, but does not feel bad about letting them get away to gain that strength. If yes and no, then you are ripe to be plucked, expect a fight. If yes and yes, then Hisoka is in a happy place, might try to be your friend, and will try to figure out how to make that growth occur. This is where Killua's brother is. Strong enough to be a worthy fight, but messing with Killua would make his brother fight even harder, but Killua might become a worth fight, so....
Basically, Hisoka is a fight junkie. I would consider him the local equivalent to Akuma from Street Fighter, though far more sociable. And a trickster/liar as well, which he uses to get even better fights.