1) Conqueror Haki/King genes (it's the same thing for me, so it all goes in 1st): the absolute strongest. Just an appetizer of Joyboy's CoC was enough to send back 3 of the strongest warriors of the WG to Mary Geoise and give chills to the probable last villain of the series. As Kaido himself (a Mythical Zoan user) commented, haki is the only thing that matters in the end, as Roger himself didn't had any DF;
3) Armament Haki: per Kaido's statement;
4) Observation Haki: per Kaido's statement. It's just below CoA because there's a CoC ability called "Observation Killing", which renders CoO null apparently, so it seems to be less important than CoA in terms of battle;
Now, the ones below depends more on the user than the ability/item per se, so I'll judge most considering a user with no haki.
5) Logia Awakening: still a speculation, but, considering Punk Hazard (the most probable result of a fight between two logia-awakened guys), it didn't seem that impressive for me. Island busting level, but Advanced CoA or CoO users could probably deal with it. The standard logia intangibility is actually more useful to a weaker user, he just can't be killed by someone without haki (unless his opponent knows his elemental weakness);
6) Mythical Zoan Awakening: it depends on the fruit, but if we're talking about broken abilities, Nika's ability to revive is one of the best of the series. Some Mythical Zoans even have pretty good abilities pre-awakening (e.g.: Yamata no Orochi, imagine that DF in the hands of a stronger user);
7) Paramecia Awakening: Paramecia is of a lower class than both logia and mythical zoans, so it's right below them. They also have long-range destruction potential (e.g.: Ito Ito no Mi), just not sure if they could be island busting level;
8) Sanji's exoskeleton: it's good, but the ones above are just probably better IMO;
9) Swords: it's too directly related to the swordsman's haki, so I'd put it below everything else; even if you're using Yoru, if you aren't strong enough, you won't be able to deal with the ones above (supposing you'd even be able to take hold of it without having top-tier haki);
10) Guns: since there are flying slashes, swords are just more versatile, although guns would be better for fodder level characters.