AoT OVA's: I Need Your Opinions! (Patreon)

Hey everyone! Without spoiling anything, could you all let me know about the AoT OVA's? When is the best time to watch each one, are they vital to the story or at least recommended to watch or are there even some perhaps better skipped? I've been hearing mixed answers online so I would love to hear all your input for me to decide how I can best tackle scheduling them in eventually. Obviously the pace at which I'm watching the show currently will remain uninterrupted. Thanks!