As a user of both (I use IntelliJ for Scala development and Spacemacs for everything else), I'd say Evil is way way better. The IntelliJ vim plugin is awesome, but it will never feel as integrated as Evil does. Emacs is way more extensible.
Embedding vim-style editing in an IDE or less extensible editor might get you 90% of what you want from Vim, but that 10% can be a dealbreaker depending on your workflow. Without easy extensibility, you might not be able to get that last 10% at all.
I'd say evil starts out a little better, maybe 95% out of the box, but now you have all the power of emacs to make up that last 5% and then start to go even further if you're not content then.