There's been plenty of world class players that have played for both Man Utd and Man City throughout the Premier League era.
The Premier League title haul proves it.
The two clubs have won a combined 18 titles between - which, you know, is quite a lot.
But who were the best players in those teams?
That's what we asked our resident Man Utd fan Scott Saunders and resident Man City fan Buvey as part of this week's Rivals.
Here's the XI they picked.
Goalkeeper & defenders
Peter Schmeichel (GK)
Buvey: "Peter Schmeichel is the best goalkeeper in Premier League history."
Scott: "Schmeichel was terrifying. Absolutely terrifying.
"He, in his own way, evolved the position in the 90s. He was so good."
Gary Neville (RB)
Scott: "Gary Neville would tell you himself that he wasn't the most talented full-back ever, but the thing that separated him from a lot of other players was his success - he won so many trophies with United.
"I think Neville is still up there as one of the best right-backs in Premier League history."
Vincent Kompany (CB)
Scott: "Vincent Kompany or Rio Ferdinand?
"I think Ferdinand is probably one of the finest defenders in Premier League history, and he won a bunch of trophies as well."
Buvey: "I think Rio had similar defensive qualities to Kompany, I also think they were just as good as one another on the ball. Rio could've played for Guardiola."
Scott: "I'd pick Rio, but I'd be willing to negotiate."
Buvey: "That's acceptable. I respect Ferdinand, but it's hard to say that Ferdinand would've carried a team the way Kompany did at Man City."
Nemanja Vidic (CB)
Scott: "Nemanja Vidic was an absolute mountain of a man. United spent a long time looking for a centre back partner for Ferdinand, and he took a little while to adjust, but he became a colossus and scored a massive number of important goals for United."
Denis Irwin (LB)
Scott: "I loved Denis Irwin as a kid. He could play left or right, he could take penalties, he was so good at set pieces, his delivery was amazing.
"He's one of those players that is kind of forgotten by this generation. For me, and I know this is getting United heavy, I'd have to put Irwin in."
Midfielders
Yaya Toure (CM)
Buvey: "So it's Yaya Toure or Paul Scholes."
Scott: "This is the first one where it might get a bit nasty."
Buvey: "I think that Toure was better at more aspects of the game than Scholes.
"One big shining light for Scholes was how he controlled games, but his best ever Premier League assist tally was eight in one season. Toure could get 15 plus 20 goals on top, and I think he actually could control a game to the same level as Scholes.
"He was good off-the-ball, he was a better goalscorer - he was a better all-round midfielder."
Roy Keane (CM)
Scott: "Roy Keane was my favourite player growing up. There was a patch of time in which he was absolutely amazing.
"His ability to drive that team forward is unlike any captain that I think the Premier League's ever seen."
Kevin De Bruyne (AM)
Buvey: "Kevin De Bruyne vs Eric Cantona."
Scott: "How much of a fight are you going to put up here?"
Buvey: "A big one. Cantona was a big name, he was that first pillar for Ferguson but De Bruyne is a better player and has more longevity."
Scott: "Cantona was the man who had the responsibility on his back to take a generation of youth players to all the success that they had. When he left they had managed to learn enough from him to be successful without him too.
"I don't think that United win as many trophies as they did in the late 90s and 2000s without Eric Cantona."
Buvey: "On a technical level De Bruyne is better on the ball, better at controlling the game. For me De Bruyne is head and shoulders above Cantona."
Forwards
David Silva (RW)
Buvey: "David Silva has 10 years at City, whether it was Mancini, Pellegrini or Guardiola, he was the best playmaker in the Premier League. He controlled games, scored big goals and the stats just don't lie with him."
Sergio Aguero (ST)
Buvey: "Wayne Rooney was a better player than Aguero, you could put him at left-back, in goal, wherever. I think he's the best player to ever come out of England.
"If you want a striker though for this combined XI it would be Aguero though. He had a better goal return per game so I think he gets in."
Cristiano Ronaldo (LW)
Buvey: "I'd say that Ronaldo may be the best player in the history of the Premier League."
Scott: "Obviously the Ronaldo that we see now is the Ronaldo that United had in that period of 2005-2009. That was when he was at United and at his very peak, then he actually elevated his numbers at Real Madrid.
"Ronaldo won the Ballon d'Or at Man Utd."
Buvey: "During that first period at Man Utd he was unplayable."
Source : 90min