I'm inclined to say Outcasts. Corsairs and BHG are obvious candidates due to ZoI and PVP, and Liberty being newbie central certainly leads to its own share of faction abuse.
But!
It doesn't matter. You'll get crappy players, but you'll also get the good players that make the game worth playing. So why worry about the worst? Look for the best instead.
Actually, I do want to add as a former member of the Order official faction I did see a fair amount of players who were, how shall we say, RP light. I will also say though that most of the corsairs I have encountered in the corsair primary ZoI have been pretty good, it's some of the others I have had more bad experiences with.
I'd say the BHG, Corsairs, and Outcasts. It seems pretty straightforward. They're groups with the biggest ZOI and the biggest ships - there are just more opportunities for problems. Those giant populations certainly add to things, yeah? They have lots of good players, too, though.
I vote [Admin] faction, nothing but lolwuts flying around in the best ships, with the best guns and best shields. Using their ill-gotten powers to do nothing useful. We should have them all banned.
I have no serious answer.
Saint Del is considered a holy healer of diseases of children, but also as a protector of cattle.