I'm just going to delicately chime in on the discussion between fish and st8.
Let's just look at the last 2 years. When it comes to season analysis between Favors and Millsap, I do think they are very comparable. During the season when the grind is ongoing, they perform about the same. My respect for Millsap lies with his play in the playoffs. During the season, Hayward is the alpha dog which gives Favors a chance to shine. We don't really know what role Favors would play in the playoffs.
For Atlanta, it is abundantly obvious that Millsap becomes the alpha. He does everything from posting up, passing out of the post, taking bigs off the dribble and shooting 3's. He is the main reason Atlanta went from barely making the playoffs to winning the East #1 seed. When he left Utah, Atlanta pretty much swapped Joe Johnson for Millsap. A former multiple All Star for a guy who was used all over the place in Utah. Ever since he's been in Atlanta, they have been conference contenders. Honestly, I don't think that Atlanta roster is that good at all. Teague is overrated. Bazemore reminds me a ton of Hood, but he's more raw in my opinion. He makes a ton of dumb decisions. Horford does everything you want a center to do, but he doesn't do anything at an elite level. He can't spread the floor outside of elbow jumpers and he's just a good rim protector and rebounder. Korver is losing a step and can be stopped if you stay on him like Cleveland does in the playoffs. He can be a threat, but that depends on what you put around him. So at the end of the day during the playoffs, Millsap is left to play out of his mind for Atlanta to have a chance against a team like Cleveland. He just didn't have enough.
I personally just prefer Millsap's versatility. Exum/Hill, Hood, Hayward, Millsap and Gobert is a contender. You have 3 guys (4 if Hill is in) who can shoot the 3. You have 4 guys who can dribble and penetrate. You have great length and defense. We would have better rim protecting with Favors hypothetically, but Millsap excels at jumping passing lanes leading him to have one of the highest steal rates in the league. That's why he was 2nd Team All Defense. Millsap is also better at guarding wings off the PnR.
We could argue them all day, but the discussion would come down to size, potential and age versus versatility, experience and veteran leadership. I would be fascinated to hear what Gordon would think off the record. Would he want his current teammate or does he think he might have a better shot with Millsap and Korver?