I'm going to make a brief stab at the much higher levels of gameplay here: the admirals and the old farts.
Ok, let's get the first things out first: the old farts (Garp, Sengoku + Rayleigh) are living legends, and forces of power in their own right. You could desirably debate that each of them is on par with Whitebeard even with the age disadvantage.
However, let me stop you there. Legends are those who have acredited a long history of accomplishments through their life, however if WB showed us anything it's that power does not last forever. We have seen samples and notes by most of the older generation that they are no longer near their prime. Garp said it whilst throwing cannonballs and Rayleigh said it whilst holding off Kizaru.
So what's my point? I believe the admirals are equal, if not above, the old farts. I.e. I believe levels 9.5 and 9 could be easily switched. Let's take examples:
- Our earliest example of comparison would be Rayleigh vs Kizaru. We are shown that Rayleigh is able to hold off, and deflect attacks of, an admiral (an unparalleled feat at the time). However, only a chapter later a panting Rayleigh is unable to break away from Kizaru whilst Kizaru does his Kizaru joking thing. If this had dragged on, I cannot see Kizaru losing.
- Our major point of reference, and the reason admirals are seen beneath the legends/old farts, is Whitebeard. Sure, let's get it out there that Whitebeard kicked some ass. Sometimes, he kicked several asses at once. However, I know I was reading a very different battle to many people since I witnessed the desperate struggle of WB against the fit, hardened and well experience admirals. Outside of hitting Akainu in the spine and the consequental follow-up, WB did not actually inflict blood-spurting damage on any of the admirals. In fact, each admiral was able to inflict damage, or at least press an advantage each time we saw a momentary 1v1. I know many readers came out of this arc with a "OMG WB > everyone, if only he didnt get stabbed". Let me remind you, that not once in the battle did WB complain about a stab wound. In fact, WB seemed to only falter under his own health (clutches his chest whilst fighting Akainu). So then the other arguement is "If WB was still young..." Yes, but he isn't. If this was a "In the good old days", we will never be able to compare it, because then I might as well future timeskip Luffy and say "Level 11".
Ok I only listed two things, planned a bit about Sengoku and Garp, but they aren't particularly good reference points.
tl;dr: admirals (Kizaru, Akainu, Aokoji) >= old farts (Garp, Sengoku, Rayleigh, possibly WB).
P.S. I don't think Roger should be in this poll, since he's dead his level is 0. If Roger and a maggot fought right now, the maggot would eat him for breakfast.
P.P.S. If Roger is in the poll at 10, Luffy should be 11, Smoker 9, WB 10, Garp 10, Sengoku 9.5, Rayleigh 9.5, Coby 9, BB 10, Ussop 8.5, Zoro 11, Kidd 10, Luffy Jr 10, etc)