Back when I was helping manage some large fan communities we looked at a few different monetization strategies re: advertising:
AdSense was the big one, and what covered a lot of our base costs. It’s been a standard for the community since the earliest days (2000-ish). It’s worked quite well for us, but doesn’t go far beyond (barely) covering costs.
We toyed with selling ad units directly, e.g. via BuySellAds, but didn’t have the manpower or experience to pull it off effectively. Unlike AdSense there was a deeper back-and-forth negotiation around placement, CTR estimates, creative, etc…
We also looked at an in-between, having specific units sold at a specific price point managed through DFP, but again, we didn’t have the manpower for it.
TL;DR = Unless you have someone on point to manage advertising, AdSense / display networks are an easy bet. But you need the traffic for that to really pay off. This can be difficult for volunteer/fan communities.