From a consumer standpoint, I think per piece is the way to go. I might enjoy one video & think another is awful. I may only watch one ever but find value in it. Good content generates more income, not everything is a hit. Seeing a lower payout from a piece *should* incentive the creator to analyze their work a little closer. Subscriptions can provide a free pass for laziness.
But really there is a place for both. A decent full time creator will have a dedicated fanbase that will offer recurring support. Having a way to express expected payback per piece in addition would also incentivize subscribers to give a little extra for stuff they really like.
Being able to set a suggested target value per piece also makes it viable for someone who is not seeking to make content creation a career but wants to do it sometimes, to maybe see results from their work.