CJS canvas+ is generally better for smaller games due to small file size, faster loading etc.
I still prefer Crosswalk/XDK for Android, its got really good plugin options, proper full-screen immersive mode for 4.4+, positional audio (works really well with headphones) and multiplayer if your game needs it.
For my games, the smoothness advantage of CJS canvas+ is gone, I notice periodic stutters even worse than Crosswalk. I find my larger fleet battles remain smooth on Crosswalk and I have not had any complaints regarding stutters (which I notice myself, but it goes away after ~30s in-game, strange).
When I did use AdMob directly with Crosswalk, I found the fillrate was >90%, most of the time 99%. With MoPub, the banner fillrate was ~80%. I did not use fullscreen Ads so I can't comment.