definitely quality. and i'll give you an example.
so suppose you have a schedule to post, right? say, two days a week which isn't bad at all. you start off with a lot of time, and you're able to make great quality videos and post within the deadline. and then, you don't have time anymore.
so you decided to keep going because, well, that's the youtube algorithm, right? consistency. well, watch time also contributes to the algorithm, and it contributes MORE. so if people aren't staying because you're posting on the right days but your videos aren't as great as they were before, people would start to not enjoy your content and youtube will see this and won't put out your content farther for new people to see. if your content is good, however, even if it takes awhile, it's more likely for people to watch to the end and youtube senses this. i can prove this by YouTubers who take a huge hiatus for a few months, and then come back and still blow up.
hope this helps!