easy. it's gotta be AB and Smart with IT4 off the bench. The backcourt picture is a lot clearer than the frontcourt.
Statistically, IT/Smart is BY FAR our best backcourt (I did a long post on this a few weeks ago). AB is statistically bad in every lineup.
People fear IT is a defensive liability, but this is WAY overrated. He is a big plus when on court due to two facts: He adds a lot more on offense (elite penetration, gets to FT and knocks them down, good 3pt, GREAT pick and roll) than he detracts on defense. Both his offensive and defensive numbers are also inflated due to PACE.
Smart has the size and defensive chops to guard most shooting guards in the league, and very few PG will post up IT (I think there are like 3-4 PG who do this on a high level), so his size is not that big a problem.
We can't EVER have IT and AB together since AB cannot guard big shooting guards - of which there are PLENTY....