Depends on what you call "good".
Banner ads via Pode's iframe and for example Leadbolt as provider work on Crosswalk APKs.. I was surprised to find that working (several people claim that it does not), but I'm looking at a running app serving ads this very moment.
The tutorial posted on here using Pode's iframe plugin has a live game example on Google Play, yes it serves ads within the frame, but if you tap/click on the ad itself a new window does not appear with the advertisement. Even if Leadbolt approves your app this can be a problem down the road.
Is the best bet to serve ads right now really only CocoonJS? This is such a great product but I need to monetize the games I create using this tool!