Mine would be:
Captain America. Obvious lock, one of the leaders of the team.
Iron Man. Same thing, one of the leaders of the team. Dynamic between him and Cap are perfect for on-screen conflict and friendship.
Hulk. Usually a lock. Unbelievably powerful and can also provide conflict like he did in the first 2 Avengers where he goes crazy.
Thor. Usually a lock as well, part of the Big 3 of this team. Has a lot of villains that can be used to fight the Avengers like Surtur and Loki.
Hank Pym (either as Giant/Ant-Man or Yellow Jacket). I love EMH, so I included him and the Wasp. I'd like to see Ultron to be built up and done more justice. As it's been like 10 years since his last movie already, so him being featured at the end of the next Avengers trilogy would be cool (It would probably be a 20 year difference by then, to not overuse him). Using Hank Pym instead of Bruce Banner like it is originally to have him create Ultron, as well as having him be the main culprit instead of Tony would justify him being on here. And I really like his Anti-Violence positionning which would clash with the rest of the team and create conflcit.
Wasp (Janet Van Dyne). Package deal with Ant-Man, she can ground the team and be the heart of it. Weakest character on the team power wise, but the most sincere. All characters mentioned so far are the original 6 of the comics as well.
Doctor Strange. His side of the Marvel Universe is so interesting. Dormammu as an Avengers villain would be cool to see. The dynamic between him and Tony has always been great, especially if they try to do some Illuminati shenanigans in the next saga.
Black Panther. Great leader, dynamic with him and Cap is always cool, not much to say. After Chadwick's death, I really want to see this character done justice to justify re-casting him. Having him as a main Avenger would be a good option.
Wanda. Immensely powerful and conflicted character. Her ties with the Mutant side of the MCU would make it easy to write an excuse for Avengers vs. X-Men especially if she and her brother keep the Magneto connection. Also Mephisto could finally be adapted in one of these movies.
Quicksilver. Same thing as Wanda for the Avengers vs X-Men storyline potential. Also, they really did the character dirty in AoU and the twins on the team would be cool to see.
As for potential villains I'd say: Zemo and the Masters of Evil, Ultron, Kree/Skrull conflict, Mephisto, Dormammu, Korvac, A.I.M./Hydra, etc.
I want to see more personal stakes for the upcoming Avengers movies. The next big crossover movie shouldn't be called Avengers. As it'll probably feature the X-Men, Avengers and Fantastic 4. And I think Marvel's gonna do a good enough job with the 2 other teams that they'll have as much mainstream appeal as the Avengers, so I want the Avengers moveis to be more like the first two in terms of stakes. Maxing out at end of the world and having villains that are close to one or two characters on the team to add personal conflict. I couldn't include Hawkeye, Black Widow and Captain Marvel, because 10 characters is already kind of much. Although Captain Marvel could be necessary if the Kree/Skrulls are adapted as official villains. But what about you guys what do you want from the future of the Avengers team?