I think the real question is if Mars is even viable to live on, as it’s smaller than earth and cannot hold the same level of atmosphere. The most we might ever really be able to do with it is use it as a place for robots to build things.
I’ve read that there isn’t enough material in the asteroid belt to significantly increase Mar’s mass enough to be able to hold a thicker atmosphere.
IMO the only way to live anywhere in space is to build airtight underground caverns. Heinlein probably had it right in “The Moon is a Harsh Mistress.”
Probably the easiest planet to live on aside from earth. Obviously we would be mostly underground. There is at least some atmosphere which will help. Plus the rovers are finding ambient surface radiation much lower than expected.
Titan is smaller than Mars and has the densist atmosphere outside of the gas giants.