Rumors around the web are saying that Marvel will do a Civil War Version story arc after Age of Ultron. Looking at various claims and evidence of info behind the scenes of projects in development it seems this is very likely and possible that they will. I'm just saying in my opinion who is likely be the members on Captain America's team. And the one's who will stay or join Tony.
Captain America's team-The Secret Avengers
He is captain america's new partner and at the end of Winter Soldier he was accepted as a friend and ally. (He is willing to fighting an evil organization with Cap and help Steve find his best friend, NOW THAT'S A BOND THAT WON'T BE BROKEN!!)
2. Black Widow
As we saw in Winter Soldier.She and Steve finally trust each other.And we from the Iron Man 2 and The Avengers, Tony DOSE NOT TRUST BLACK WIDOW YET. Plus she more relatable to Steve's personality over Tony's.
3# Captain Marvel/Ms.Marvel Carol Danvers
There's two reasons why Carol is likely on Captain's Team instead of Tony's. 1# Since Tony and Banner are the Science Bros and they have a strong friendship, Hulk is likely to stay with Iron Man. So Captain America needs muscle on his team if down the line the two teams are going to fight . 2# She likely going to have a connection with Thanos or Adam Warlock (Easter Egg in Guardians of The Galaxy) for the Infinity Gauntlet Arc-Phase 4. And the whole military background will give her and Steve something they relate to.
Since the science bros are on one team. Captain America is going to NEED a scientific genius on the team when things get tricky and science & strategy are needed to solve the problem.
5# The Wasp-Hope Van Dyne
The daughter of the original Ant-Man, Hank Pym and the likely partner of the 2nd Ant-Man, Scott Lang in Marvel's Ant-Man.She probably still be at his side at or during the civil war.
6# Black Panther
T'Challa Udaku is the king to Wakanda, richest country in the world due to the rare metal Vibranium can only be found there.And as we know from the Comic-Con teaser Captain America shield gets cracked and that's only place where they can the metal.So it's obvious that either Scarlet Witch uses her powers to fix it or they go to Wakanda.And after some talk and help against the enemy.Black Panther enters the Secret Avengers because why would he trust Tony Stark when he's the one who cause this problem in the first place. Endangering the world and trusting his weapons to protect the world like Hydra thought they were doing.So team Cap it is.
I don't list Bucky because he's seem too deep as as solo character rather than a team player even though he knows that he and Cap has a past together.And it makes his story and journey more complex as he does things on his own .
Iron Man's Team-The New Avengers
1# Bruce Banner/The Hulk
Science Bros .As we've seen with the end credit teaser in iron man 3 and the info and images from Age of Ultron ,the duo are pretty much best friends.
He's a god its seems that he's a better fit besides The Hulk, the strongest and Iron Man, the smartest.Plus all the characters on Cap's team are more human and grounded which not real fit for the God of Thunder.
In my opinion The Avengers needs a very human character to make it feel whole.And this will bring tension between Widow and Hawkeye.This will make it feel more dramatic in The Civil War as friendships and relationships changes
4 & 5# Scarlet Witch & Quicksilver
They are twins, they have been tortured by HYDRA and they are family so it seems they would stay together after the team's falling out and stay with Tony.
It's Jarvis in a body. Team Tony all the way.
# War Machine
Even though he is Tony Stark closest friend.I believe he's going to get killed off in Age of Ultron in a dramatic way.I have 3 reasons why he will die. 1# emotional impact to the characters and the audience. 2# He's a supporting superhero and NOT a core Avenger.It can't be Falcon, Scarlet Witch, Quicksilver or Vision because they just got in the MCU.Rhodey been around for a while And Thor, Iron Man and Captain America are still contracted to Avengers 3.3# He has to die to show that their are real deaths and not fake -outs in The MCU.
I have no idea about which team Dr. Strange should join.Or he should just stay neutral in the Civil War.State in the comments about where Strange should go.
1.Captain America 2.Falcon 3. Black Widow 4.Captain Marvel 5.Ant-Man 6.Wasp 7.Black Panther 8. Bucky (If he joins)
The New Avengers
1.Iron Man 2,The Hulk 3.Thor 4.Hawkeye 5.Scarlet Witch 6.Quicksilver 7.Vision 8.War Machine ( If he doesn't die in Age of Ultron)
The War of Gods & Men