goku has a 2.1x AP advantage here, but miyabi has a pretty substantial LS advantage. since both are in character here i don't really see either trying to kill the other, so i think both would likely just go for incaps via KO instead. i think goku would probably just be more skilled than miyabi even in this key, and he'd have the general edge in CQC. miyabi does have higher LS, but she doesn't really go for things like grapples or restraining in character, so i don't really see her utilizing it to her advantage even if she was just trying to incapacitate goku with a knockout
both have enhanced senses, both are exceptional acrobats, both are masters with their designated weapons, and both have accelerated development, though i would say goku's is definitely more useful to him here as he grows stronger in the heat of battle. goku wouldn't really be able to replicate any of tailless' abilities so i don't think his power mimicry would help him much. ki manipulation would help him fight from afar, and the solar flare i think would actually be a pretty vital asset to him. he also has both nimbus and the power pole to also fight ranged on top of giving him a lot of good mobility. he also has a general stamina advantage, so he'd likely be able to outlast miyabi in a battle of attrition (i think miyabi's stamina should honestly be higher, but that's something i'll probably have to get a CRT done for)
miyabi can boost her own stats, can inflict stuff like freeze and frostburn onto goku to debuff him, and she can still fight and act even while unconscious. if given ample time to charge up, miyabi's hollow splitting attack could definitely one shot goku, but that's :
1. assuming it even lands in the first place
2. assuming goku gives her enough time to charge it up (which i don't think he would)
3. assuming miyabi would even resort to using it to begin with (given she's in-character here, i doubt she'd go for an all out attack trying to kill a child)
funnily enough, goku's tail is also a notable weak point for him in this specific key, which i think is something miyabi could take advantage of.
not gonna cast a vote just yet because i want to see more arguments but this does seem pretty interesting. i'll probably have to mull on it a bit more but if i had to side with someone at the moment, i'd maybe say goku? i think being stronger in CQC on top of having good mobility options + superior stamina helps him a good amount