Horford could easily end this and have his people "leak" that there's no chance he goes back to ATL, but I really do think he wants a full 5 year max from them. All of this "Boston and Washington are frontrunners" is probably just a smoke screen by his agent to put more pressure on ATL. Why else would he tell them he's making a decision by this evening? It's a deadline.
I'm sorry guys but if it waddles like a duck and quacks like a duck, it's a duck.