Raven’s antispam – powerful and invisible fighter against comment spam. No set-up necessary, install and forget.
<h4>Details</h4>
Visitors with enabled JavaScript (99%+) see nothing – no annoying questions, no captcha, nothing. (Users with disabled JS see an additional text-field and a word that must be rewritten into the textfield.)
Note: this plugin is not able to check your trackbacks – to handle trackback spam, it’s necessary to use some other solution. (I recommend to disable trackbacks globally, since they rarely bring any benefit for your readers.) <a href="http://kahi.cz/wordpress/ravens-antispam-plugin/" rel="nofollow ugc">more…</a>.

Raven's Antispam

Powerful and invisible fighter against comment spam.

wpsimpletools

Completely disables comments functionality from backend and frontend: 
* Hides existing comments 
* Close comments on the front-end 
* Disable support for comments, trackbacks and ping 
* Redirects any user trying to access comments page 
* Removes comments metabox from dashboard 
* Removes comments links from admin bar 
* Removes comments page in menu 
* Completely disables comments API

Disable Comments

The type of plugin I just love... does exactly what it says, no configuration necessary, source readable and understandable in minutes.

Simple, effective, no config ✅

Completely disables comments functionality from backend and frontend. Just install it, nothing to configure!

Raven's Antispam vs Disable Comments