Avatar. It'll (presumably) have a gigantic budget and join Rise and RSR as one of the resort's flagship modern attractions. Shanghai's Pirates is somewhere around 8 minutes long and looks like a masterpiece; if DCA's Avatar is similar, it'll be a game-changer for DCA.
I'm less confident Disney will invest sufficiently in the Coco boat ride. I have no evidence for this suspicion, I'm just cynical. On paper, a Coco boat ride would be the most exciting of these forthcoming attractions for me -- especially if it's long, filled with AAs, features a small drop, and (as promised at D23) takes some design and storytelling cues from Disneyland's Pirates. In reality however, I'm expecting something more along the lines of DisneySea's Tangled boat ride; not bad by any means, perfectly competent -- but predictable, safe, and forgettable.
Marvel is not interesting to me (no offense to anyone who enjoys it) so the Avengers attraction ranks last. However, I'm very eager to see Avengers Campus grow into a proper land, so I'll be glad to see these 2 attractions finally open.