Asami. both were far more compatible and healthy. the strings only came apart with korra. Its likely they could have fixed their issues if mako were mature and upfront about it but his actions caused them more strain.
As adults I'm almost certain they would be great together.
The main problem with mako and korra was that they had base level attraction and maybe infatuation but they had little chemistry and were shown to clash with each others personality. they then decided to make that a relationship. on top of that, mako, being a government officer and korra being an avatar would also put stress on them because mako could not always support korra and korra coudl not always respect mako's work.
(some say their relationship was abusive but I wouldn't go that far, its extremely toxic but not abusive)
