I’ve been fighting spam on my sites for too long: recent stats tell me that out of all 2640 comments that I received in a given period, only 14 of them were real! So 99,5% of my blog comments are spam and only 1 in 200 are real. I’m happy to announce that I have finally found a solution that seems pretty damn watertight:
CleanTalk* is a business that offers plug-ins for many platforms (including WordPress and phpBB) and it’s honestly the first software ever that succeeds in reliably stopping the flood of spam on my sites. Best of all, it does it completely without bothering the user with silly tests – and it. just. works. correction: 
unfortunately my initial setup blocked some comments but I found them in the logs and the CleanTalk support staff quickly helped me resolve the problem (see thumbnail on the right, click to enlarge), so all is well. I’m still keeping an eye on the logs though – but even this is so much better than all other anti-spam plugins I’ve tried so far.
I’m very happy with this now. Of all the thousands of comments and registrations that were attempted since I set this up, no spams were published, and no non-spam (“ham”) was blocked. Only 2 spams got through CleanTalk and were subsequently placed in the WordPress review queue. “Two” being a manageable amount to deal with in WordPress, it was easy to reject them.
The 14-day trial was more than enough to convince me to sign up for a year – especially because it’s ridiculously cheap at around $8 per year! Considering the time I spent dealing with spam - and testing anti-spam plugins - that makes it easily worth the money. I’m glad that I don’t have to handle the spam myself and that software can do it for me – reliably! Other anti-spam plugins just weren’t good enough.
Incidentally, the stats seem to show that the number of spam comments are going down – perhaps the spammers are noticing that their efforts are blocked? Nah, probably just a coincidental and temporary dip in spam combined with my own wishful thinking.
Update 6 months later:
This is still awesome – more than 10.000 spams have been caught, and zero have been allowed through. I am very impressed.