In reply to John Matras.

I'm perhaps not the best person to ask, since I'm biased as I created my own anti-spam plugin ;)

https://wordpress.org/plugins/spam-destroyer/

I get about 100,000 spam messages per month. That plugin used to whittle it down to about one spam every six months, but that has shot up to about five per month lately. Using Akismet would probably get rid of those last few spams, but I prefer not to use it as I figure if my plugin isn't blocking stuff then it's just a sign I need to make my plugin better :) (I'm working on a big improvement for it at the moment, which seems to be working well so far, but isn't ready for public consumption just yet)