If you have a point guard, who's strong point is scoring like Jackson, he will blend very well with a Marcus Smart type of skill set. Marcus having decent point guard skills will help Jackson to be who he is.
Someone has to play defense in the back court. All teams should have a strong back court defender. Marcus can cover either PG and SG, and disrupt opposing offenses. Plus Smart will end up a decent scorer as he develops.
Bradley is who he is, he defends well, he's a streaky shooter, a hard worker, he would look best coming off the bench.