Now that we have members from the Iron Man movies and Captain America movies all into one, there is going to be some controversy on the fan favorite of the movie.
Black Panther is definitely going to be THE fan favorite and if not that then one of the top 3 because from the trailer... Black Panther is just pure savage, from the way he chases down Bucky on the motorcycle to him testing Captain America's strength in the following picture... you know he's getting fan's excited to see him in action and I can't wait to see him either.
Next we have the one and only... Spider-man. Even though this isn't his first movie we have seen him in, we have never seen him with any of the Avenger's before. I think he has the opposite but same effect that Black Panther has with the fact that we only see him once in any of the trailer's, which leaves anticipation and excitement to see what impact he will have on the entire battle. The surprise of him showing up in the airport battle is really going to have people on the edge of their seats.
The last possibility for a fan favorite could be debatable, but I would have to say Ant Man. I think he will most likely have the same effect as Spider-man being under shown in the trailers leaving us with anticipation. He was a great character in his own movie, and I think fan's are going to love to see the funny Paul Rudd in action again fighting for Captain America's team.
Please keep in mind these three characters are just my opinion the top three fan favorites. If you think it might be someone else put it in the comment section!