We use Cloudinary at work and I would recommend it to anyone, I think it's an awesome service and the API is really easy to use.

They offer a pretty generous free tier for personal stuff as well, although I wish they had some plan that was between the free tier and the $99/month cheapest one, which is quite a steep increase from paying nothing.

This came to mind for me as well, as it's something I landed on in the past for managing UGC. The primary benefits being a decent api and administrative interface for moderation. It's certainly not perfect, but there's not a lot of competition in the space that I could find. I think most devs lean towards DIY.

Or https://www.simplefileupload.com/ (good if you're on Heroku) or Uploadcare or any of the many other services that help do this kind of thing.

Imagekit.io is good too

And filestack.com