My vote's for Bamba.
In the short term you could bring him along slowly to develop under Horford's wing. Much less disruptive to our rotation than Porter Jr would be and could valuable in matching size against some of the bigger teams out there like Detroit, Philly, and even Toronto.
In the long term I believe in the talent. A fully developed Bamba in contention for best defensive big in basketball. Give him a few seasons under professor Horford's wing, lock him in the gym shooting 3's in the off-season and you might just come out with the type of Monster that makes us a matchup nightmare against most teams and allows Kyrie, Tatum, and Hayward to feast knowing the defense is covered.