Orlando &/or his Crip associates.
Tupac ran his mouth & swung his fists without thinking.
The Suge thing is a no go simply for the fact that the fat bastard was sitting next to him. & don't start with, 'but that's the genius of it...' - bullshit.
Although Tupac may've had the potential to be, he wasn't that much of a threat to the US Government & while I think they could've been keeping tabs on him, I don't think they would've been concerned enough to kill him.
Puffy's a snake & Biggie was scared & humiliated but I don't think either of them did it.
The Black Mafia may've had a vendetta against Tupac but I still can't see them killing him in Vegas & the way shit went down was actually sloppy. Not saying that it would've been a top notch professional job if the Black Mafia were behind it, but the chaos of the situation, IMO, implies a impulse killing.
Anyways, for me, Orlando & the Crips are the ones who done it & the problem that a lot of people here seem to have in seeing this, is that you cannot accept that Tupac died for something so petty & there was no grandeur surrounding his death.