Atlanta
Horford
for
Miami
Whiteside
Winslow
McRoberts (salary dump)
Stokes (trade filler)
Why for Atlanta? Horford is in the last year of his contract and not only is there concern he won't re-sign, but rumors swirl that the Hawks are considering a reset. Whiteside is expiring, but the Hawks would have the cap space to re-sign him to be their center of the future. The promising Winslow fills the void left by Carroll. McRoberts is a salary dump, but he could have value in Bud's pace and space system if his health ever returns.
Why for Miami? The Heat are in serious danger of losing Whiteside for nothing this summer. While losing Winslow hurts, Riley is in win now mode. Horford is in his prime and fits the current core's window (Bosh, Wade, Dragic). It's a risk, but it's hard to envision Riley losing Horford this summer. The Heat would have the ability to pay him max money since they're also sheding around 8.5M in cap next season by trading away McRoberts and Winslow. The Heat's crunchtime 5 of Bosh, Deng, Horford, Dragic, and Wade would be pretty formidable. Plus, they could potentially add depth with soon to be player buyouts.