I'm guessing the Pelicans will insist on both Tatum and Brown in a deal, along with picks. The choice won't be up to us if we want AD.
Talent-wise, Brown is the guy you would want to keep between him and Smart.
But, if the goal is a lineup of AD, Horford, Hayward and Kyrie, then guys like Smart and Morris fit much better into supporting roles for that group than guys like Brown and Tatum who want to get their own leading roles and big pay-days.
Chemistry-wise, moving Brown over Smart would make more sense.