Itachi wins, mid diff.
Once Mu goes invisible, Itachi will know that camping in Susanoo won't help him, so all he needs to do is make a few crow clones and then wait. If Mu attacks one, he simply uses Amaterasu right in that spot (or if close enough he spawns Susanoo's hand and grabs him), and being invisible is irrelevant since Mu still isn't fast enough to dodge it. The clone bursting into a flock of crows can also be used to confuse/distract Mu and sensing isn't going to let him tell which is the original when Kabuto (better sensor than Mu by a lot) got feinted by Itachi's Crow clone. Itachi would win the waiting game here if Mu tried to play it since Itachi standing idly doesn't use chakra, but Mu flying and maintaining his invisibility uses chakra.
If he switches the strategy and tries to murk with Jinton, then he gets raped by Amaterasu the moment he becomes visible.
