Re: Where should the Maximoffs appear first?
Avengers 2. I don't think they should appear in a cameo a la Hawkeye in other MCU movies, and there won't be any reason for them to show up in any other movie anyway. I would've suggested Cap 2, but their cast is already bloated enough as it is; adding in SW & QS would've turned it into X3.
Steve Rogers: "You're my friend"
Winter Soldier: "You're my mission"
Steve Rogers: "Then finish it, because I'm with you 'til the end of the line"