Well lets see.
-Mei's Lava has partially melted the weakest version of Susanoo, and by partially I mean barely.
-Son Goku's Lava has burned KCM Naruto's face, but it's the same Lava Mei is using but Yonbi can use it in much much greater quantities and he's a Bijuu.
-Amaterasu burned the shit out of B in Bijuu Mode. It incinerated Danzo in a matter of seconds. It also burnt a hole in a giant toad's stomach in a split second. It's also >>> regular Katon, but so is Lava.
Amaterasu at it's strongest is the best technique and it's best feats are far superior to any Lava's best feats. Amaterasu would eat up any Lava jutsu if the two were to clash.