If you are already considering the AGPL, I'd like to suggest the EUPL. It also covers SaaS, is copyleft (forbids nonfree forks), but non-viral (can link to nonfree software), a lot easier to read, and also doesn't have the "bad name" some people attach to the GPL family.
I can't speak to how well it fits in your usecase. There are too many ways to do monetization, and I don't know which one you have in mind. But copyleft at least stops other entities from monetizing without sharing their contributions, so if you want to keep it open source, that's my recommendation.
I can't speak to how well it fits in your usecase. There are too many ways to do monetization, and I don't know which one you have in mind. But copyleft at least stops other entities from monetizing without sharing their contributions, so if you want to keep it open source, that's my recommendation.