I’d rather a service be funded by ads, because if not, they’ll have to find some other way to make money, which could include:

• Paywalling - I won’t use it then.
• Selling your personal information egregiously - I don’t mind when a company has the information I give them, but if they’re relying on selling it as their primary income, it’s probably going to lead to something shady.
• Cryptocurrency mining - I don’t want my computer to heat up while I’m trying to watch YouTube videos, as I often do that to let my computer cool down between games.