On paper, it's Jones by a clear margin. It comes down to how much you hold his PED controversies against him.
After that it's harder.
I'd put GSP and Fedor in the next bracket together. Fedor for going undefeated for so long in a division where one punch ends a fight, and GSP for being the most well-rounded fighter ever (alongside maybe MM) along with his longtime divisional dominance and avenging all of his losses.
Anderson would come next in my book. Not as well rounded as the 3 above him and certainly had some PED controversy like Jones, but probably has the best highlight reel in MMA history and at his peak had IMO the best aura of invincibility. His win streak was incredible also.
Demetrious is next. He's a very hard one to rate, as I could see someone making the argument for him being #1, and him being #6. The knock against him is I feel that his division just wasn't as built up with as skilled of fighters that the others on this last had to face. Maybe that's just lack of name value of those fighters, but that's how I see it.
Khabib is another one that is hard to rate. On paper - he's perfect, and probably the most dominant fighter in MMA history (i.e. barely lost any rounds, never hurt). He just doesn't have the long-standing dominance that the others on this list have. He retired after 3 title defenses - many of the fighters on this list have 6+.
I love Jose Aldo, one of my favorites on this list. I just think there is now too much cloudiness around who is actually the best FW of all time (with Max and Volk now also having great runs) so it's hard to have him above anyone else here.