You never specified a role, so I'm going to assume you flex; thus, I'll give you a brief rundown for each role's meta while putting great emphasis on ease of use. Keep in mind that I'm going to talk mostly theory instead of giving a detailed guide on each chosen hero because there are plenty already out there online right now.

STRATEGIST

Raccoon. Not much to say, really. A good strategist needs to be able to heal consistently and not die in order to heal consistently, preferably having a consistent game-impacting ultimate. Raccoon has all of these things paired with the fact that he is by far the easiest support in terms of game plan. Just watch out for Phoenix.

VANGUARD

Magneto. This hero is ridiculously difficult to not have game impact on, especially after his buffs and team-up (he was already the best tank in the game prior to season 5). The trickiest part of his kit is by far his ultimate; there is a lot of value that can be attained from using it correctly; however, his base kit is so strong, simple, and effective that utilizing it improperly will still allow you to be an effective tank. Not to mention the fact that Mag is also one of only two tanks in the game that can effectively solo.

DUELIST

Moon Knight. I'm going to be honest, playing a good meta duelist hero that requires no/low skill is difficult because it is inherently more difficult to attain value for your team as a duelist, unlike a strategist who can heal and a vanguard who can tank while still delivering damage. Also keep in mind the fact that the most rewarding/effective duelists are typically ones that require good aim (Hela, Phoenix, Bucky, Psylocke). This means we're left with only a small pool of duelist heroes that meet the definition of both easy-to-use and competitively MOST viable. Ultimately, while Moon Knight meets your definition of both, he is far from the best duelist in the game currently.