I would pick Harden if he is committed on playing defense. Harden is my first choice as a player to build around. But I would pick Smart as a championship piece. I believe that we are just another IT away from contending. And now rim protection has improved with the addition of Horford. Adding Harden (without commitment to d) and removing Smart will just be an offset.
So this is what I get:
one more IT= add a player that can create his own offense(and hopefully be taller than 5'9'')
Smart= just as valuable as Harden would be for us
Have you ever considered trading a second round pick for Tony Allen.....he's basically/was Smart but without the potential for a really good shot.
See Memphis. Have they won a ship? No, but neither is Harden. But they were 50+ win team every year with TA as a starter. And he is one of the major pieces off the bench during the Big 3 era.
There is a reason why Spurs retired Bruce Bowen's number. And Pistons won with Tayshaun Prince as a starter.
Are they better than Harden? No
Are they a better fit on their team? Yes
The reason why the Grizzlies were a 50 win team? Because they had Conley, Randolph and Gasol. Did Tony Allen contribute to that? Of course, but if you think they'd have had the same success without Conley, Randolph or Gasol you are dreaming.
The reason why the Spurs won so many titles? A combination of Robinson, Duncan, Ginobilli, Parker and Leonard - as well as Popovich. Did Bruce Bowen contribute to that? Of course, but if you think they'd have had the same success without Duncan, Parker or (later) Leonard, you are dreaming.
The reason Boston were dominant in the big 3 era? Rajon Rondo, Ray Allen, Kevin Garnett and Paul Pierce. Did Tony Allen contribute to that? Of course, but if you think they'd have had the same success without Rondo, Pierce, Ray or Kevin you are dreaming.
The reason the Pistons won a title? Chauncey Billups, Rip Hamilton, Rasheed Wallace and Ben Wallace. Did Prince contribute to that? Of course, but if you thing that team would have one the title without Billups, Hamilton or Wallace you are dreaming.
The same is true of Derek Fisher on the Lakers - he was a huge piece for that team in a number of their title runs, but without Shaq/Kobe/Gasol there wouldn't have BEEN any title runs.
When Harden was in OKC, there were a championship contender - but that team also had Westbrook, and Durant, and Ibaka.
When Harden went to Houston he's game leaped to a whole other level, and there is no question he made that team a lot more competitive the moment he got there. He single handedly won games for that Rockets team. When Dwight joined their record skyrocketed, and the were good enough to be considered a contender for a good couple of years there, despite the fact that Howard was being criminally underutilised.
Every great team NEEDS it's hard nosed role players. They all need a guy like Avery Bradley, Jae Crowder and Marcus Smart. But you know what? There are a LOT of guys like that in the NBA.
Every great team also needs offensive stars - guys like Isaiah Thomas, Ray Allen, Steph Curry, James Harden, Kyrie Irving and Kevin Durant. Without players like that who can take over games offensively, you'll never sniff an NBA championship...no matter how many Marcus Smart's you have. Yet those offensive superstars are a LOT rarer and a LOT harder to get then the hard nosed role players - who are everywhere.