With each movie, It seems a common practice for the Film-Makers to change up the costume of the Hero. It's a good way to get kids to buy the new action figure and it helps to differentiate one movie from another.
In the First Avenger, Howard Stark goes over Outfit options with Captain Rogers. In that scene he shows him a Carbon Steel Chainmail shirt that he says will stop a knife. They decide however on a kind of paratrooper nylon/kevlar material, which seems more practical in combat than bulky chainmail.
After Cap is thawed out in 2012, He receives an Outfit from [Agents of S.H.I.E.L.D.](series:722469)'s Agent Coulson in which the older functional style of the 1940's outfit is traded for a more tightly fitting garishly colored Avengers' outfit.
This outfit probably afforded more mobility but it seemed like he took a lot of damage in this outfit.
In [Captain America: The Winter Soldier](movie:254973), We see Cap wearing a more functional outfit with subdued colors reminiscent of his WWII outfit. The Helmet has been slightly changed to allow the ears out for better hearing. This is much closer to his classic cowl/helmet worn in comics. The outfit itself is based on the Super Soldier outfit Steve Rogers wore as Commander of S.H.I.E.L.D.
In the upcoming [The Avengers: Age Of Ultron](movie:293035) Cap's outfit has been designed by Tony Stark and bears the Avengers' "A" on his shoulders. There is more color in this outfit and it bears the most resemblance to his Ultimate Comics outfit. The helmet looks the same as his S.H.I.E.L.D. "Super Soldier" helmet.
See Also - Did we all Miss a MAJOR Easter Egg / Potential Character Set Up in Captain America: The Winter Soldier?
Now, in the Upcoming Captain America: Civil War co-starring Robert Downey Jr as Iron-Man, will Cap wear something to differentiate his appearance from those who are pro-registration? Perhaps he will wear the scale mail shirt rather than wear the shirt emblazoned with the Avengers "A" on the shoulders?
What will Cap's outfit look like then? Will it be something along the lines of his most current Avengers' outfit or will he have the Scale Mail Shirt?