I'd go something like this:-
I place Zuko above Korra & Roku for being able to output his scale & power with greater rate and efficiency while having superior Defensive power under his Amp as well--all rounded off by having the Constitution, Physicals and Tactical sense to hold that tad Rate-of-Power advantage upkeepingly better imo; perfectly get others' reasonings for placing some Avatars higher but personally feel that even SC Zuko host marginal superiority here combatively above the Base Avatars without Amps of their own.