1. Sabo -- matching Fujitora's.
2a. Vergo -- COA expert, hyped by Doflamingo himself, confirmed superiority in mastery over Smoker. Could block blades(something even Doflamingo failed to do)
2b. Zoro -- COA expert, confirmed superiority in mastery over Pica, breaking his full body hardened armour
3a. Doflamingo -- blocked a Jet Gatling with hardening. But was bleeding from grabbing a blade
3b. Younger Chinjao -- his armament haki clashed evenly with Luffy while old, so i give him the benefit of doubt while in his prime to be superior to Luffy's
4. Pica -- Experienced armament user capable of FBH. His haki has been hyped by both himself and Zoro to be able to block mountain busters cutting ability
5a. Luffy -- Could block blunt, equalized old Chinjao's armament in the initial clash, but has weakness with cutting blades, with a hardening bypassed by Hody's bite and Doflamingo going through it with his own hardened blunt force
5b. Old Chinjao -- Equalized Luffy's armament
5c. Smoker -- Could block Law's cutting ability, superiority in haki over Tashigi, but inferiority over Vergo. Not much to go on though as he could as well be even above this class
6- Bellamy -- Already admitted Luffy's haki is far above his own. Yes he bypassed Luffy's hardening once, but only because it was reinforced by his strongest attack
PS: The a,b,c is for people who i rate around the same range in mastery from what we've seen
If i were to put Law, he'd be in the second class too for completely blocking Doflamingo's string(something that dealt with meteorites before)