I would trade ANY two players on the Hawks roster for Dwight Howard.
This may strike some people as a surprise given my stated love and admiration for Al Horford, but Dwight Howard is the best center alive by a wide margin and an undisputed top-5 player in the NBA. The widespread speculation that the Hawks have offered Smith and Johnson for Howard could be correct, or it could be false. It almost doesn't matter. I can't possibly see the Magic taking on what could be the worst signed contract in the NBA right now (well, outside of Rashard Lewis) in Joe Johnson, so while on a strictly talent basis, the deal makes some sense for them, it would never happen. The underlying issue here is whether it would be a good idea to trade Smith AND Horford for Howard, and while I would do anything in my power to put a deal together that didn't feature both assets, I would unquestionably do that deal.
One note on the above statement is that the only way I wouldn't do this deal is if it was indeed both Horford and Smith AND Howard refused to opt-in in for next year. Any other package and I don't even think it matters if he opts in. A Hawks roster with Dwight Howard on it (even if he's surrounded by Teague, Joe and nothing else) has a higher upside on day 1 than the current group with no cap flexibility and a core that has (relatively) peaked. Done and done.