The best would be opt-in (or opt-out) mining to help the hosting costs. Plus it'll catapult crypto currency into the spotlight and imo anonymous decentralized currencies might be better than state-owned (or private) currencies.
On one hand, less ads -> less tracking to serve me tailored ads, less loading dozens of resources, less videos in autoplay, the money goes straight to the site I use and not to Google/Facebook/whatever.
On the other hand, running CPU-intensive processes on the browser is not a smart idea and what usually leads me to killing it as it hogs all my resources and makes my laptop overheat.
Tentatively, I'm going to say that I prefer mining over ads, slightly. I'm still going to block everything and whitelist, and I'd prefer if there was an easy way to get/make anonymous micro-donations.
Entirely? No, I don't think so. Not for big websites like facebook or google because they'd find some way to make it still track you, but for things like the pirate bay or distrowatch or other organizations whos' business model doesn't require tracking their users, I'd support that.