The problem with comparing all sprinters is that you don't know who was taking what, or what would have been optimal for any individual.
IF each athlete could have taken a standard cocktail that had a whole bunch of everything, so that their body could take what it needed and just flush what it didn't, then we could talk about each of them being optimized. Of course training would also need to take on such a character, but that's not likely. But the world isn't perfect.
If this condition was met, who knows. As it is, I personally believe that Bolt is the fastest, rivalled by many others like BJ using modern equipment on a modern surface, and Powell had he a stronger mind. Slowing to a 9.74 WR in Rieti is just about as insane as goofing and backward-leaning a 9.69 WR in Beijing. Just about, but not quite. Same with BJ--9.79 on a mushy track with crap 80's spikes is nuts, almost to Bolt's level. Put Lewis on some serious gear and what do you think? He made it to 9.86 on a hard track, but look at the obvious weaknesses in his race. Heck, if a biomechanical disaster like Coleman can get to 9.7-mid/high, then somebody with better capability like Lewis, Bailey, Gatlin, even Lemaitre, etc. would "easily" get to 9.6-mid/high, probably better.
Bolt was pretty good when he was at his best. His form was nice, from start to finish. Not perfect, but very, very good. Powell in particular was bitchin'. Look at the side-view of his 9.72 to get an idea of what 100m form should look like. In that one, he looked to actually have run through the line. Of course every 100m athlete will have their own optimal form, but Powell's could form a base standard.
Hayes to me is sort of like Coleman, biomechanically flawed--but geez, I would put him in with the other greats, better than Coleman.
Bailey was already 9.84 after rounds and a million false-starts, and a not-great start. He would have gone 9.7x in Atlanta had it not been for the false starts.
A lot of these guys run up against structural limits, which it appears that supps couldn't breach. Greene, Blake, and Gay with their hams, Bailey and others with achilles, Bolt with his back, etc. BJ had ham issues and took an overdose, and it worked for him. Bolt had Hans, and it worked for him. Blake apparently actually tore it off the bone, it didn't work for him.
I still give it to Bolt, but only just. 9.58 is no joke, he actually DID it. We talk about the other guys, but it takes a combo of supps, training, mentality, circumstance, and LUCK to actually get there. When you see a guy do something extraordinary not once, not twice, not three times, but FOUR times--9.58 (0.9), 9.63 (1.5), 9.69 (0.0) goofed, and 9.77 (-1.3)--the element of luck is no longer a factor. Heck, had Bolt gotten lucky--like running through the line with a +2.0 in Beijing--we would see 9.4x on the list right now.
That makes him #1 all-time. Nobody else we know of could touch that, regardless of what BJ says in interviews.