In answer to your original question? Both. Generally what filmmakers do is submit their created movie to festivals. As soon as the festivals have finished showing the film, they then release said film onto youtube. This is the most efficient way promotionally. Since in the film thumbnail you could boast the competitions you were in. (Ive seen this work VERY affectively). And you might have seen it too. This will pull in more viewers, also, people who saw the film at the festivals (and whom you now probably are in contact with) would probably love to support your online version. That being said, While festivals do offer a lot of professional contact and work which is vital Ofcourse, they don’t offer a very large audience, which is a problem cause at one point in your filmmaking career you MAY want to start getting recognized by more than just critics. In which case you just need to figure out the algorithm and build a fan base. Which unlike how most people say, is actually pretty damn easy and fun to do if you just know how to do it right. I hope this helped, also, what’s your film about? I’d love to know more about it.
Edit: The reason that filmmakers upload their films AFTER they have been through festivals, is because generally competitions will not show already released movies. At least not as much.