Katt, do you mean what media do we watch them on or what order to watch them? You mention a few different things, so it's not clear to me what question you are asking.
I have them all, other than CM (DVD for the phase 1 individual films, and BR from Avengers onward). So watching them is not a problem. And it seems like one or the other of them is almost always on in the background at my house.
For me, if I were to try to do an abbreviated marathon to gear up for Endgame, it would probably focus on the main infinity stones storyline and Tony, with some of the films cut out just to save time. I think it might go something like this:
-Avengers: Sets up the whole thing, and seems like it is going to be revisited.
-Iron Man III: Hear me out on this. I think the arc for Tony here is really important. The trauma he is feeling here is extremely relevant to what happens next.
[-Thor: The Dark World: Important from the standpoint of the infinity stones arc overall. But what happens in that regard is relatively straightforward, so this film is probably one of the more skippable ones in my list]
-Age of Ultron: I think going from IM3 into this one would have a cool effect in terms of observing where Tony is, emotionally and psychologically.
-Guardians: The cosmic stuff is important. Power stone. Thanos. 'nuff said.
-Civil War: The team splits. This is important for Infinity War.
[-Dr. Strange: Time stone. But probably skippable.]
-Thor: Ragnarok: Great bridge for Thor between Age of Ultron and Iinfinity War.
-Infinity War: well, duh.
With the two "skippable" films, that's still 7 movies to watch. But it is a more "streamlined" story, if you can consider 7 movies "streamlined."