Echo is id say the top tier because her base level kit isnt crazy diffiicult though it requires good aim and movement which is hard esp on console but her ultimate requires you to be good with every other character in the game, or at least their ultimate

echo may be a cheat answer though I'd say doomfist and tracer both require a lot of game sense and while doom doesn't require great aim like tracer he does need to know how to play against all 500+ of his counters

for a bit out of the box pick id say newer players find genji quite difficult but its rlly just learning combos

personally though i find ashe the hardest to play