IW is my nr. 1 for now, even though the ending isn't positive, this is an obvious 2 parter, so a final verdict would be after A4.
The 1st Avenger is on 3rd place, right after TWS.
Black Panther actually disappointed me, for some reason certain things in that movie felt too rushed in the pacing. I did like KillMonger, but also felt him rushed slightly.
AOU was a huge let down for me, the whole Scarlet Witch/Quick Silver felt out of place, also Ultron was too sarcastic, how can he be sarcastic before knowing human behaviour (which sarcasm is a part of), felt wrong to me. Also Hulk and Black Widow thingy was unnecessary.