I have been using Akismet, free of charge, for several years on 10+ sites and have experienced zero problems. I especially like its "set it and forget it" nature.
I use akismet for all my contact/join forms, saves using a captcha. Every now and then a spammer breaks through, I get a couple hundred spam and then they close that loophole. When I was checking the sites that were getting legit comments made it through with very little false positives.
I got out of bed today staring at a ghost. Who forgot to float away, didnt have all that much to say. Wouldn't even tell me his own name.
Non ducor, duco
Let me join the chorus. I have been using Akismet for many years on a number of blogs and I am not aware of a single problem. It leaves very few spam comments for me to reject. On the odd occasion when I have checked what it regarded as spam comments, I have agree entirely with the designations. I would recommend it wholeheartedly.
Akismet's been doing a good job for the most part since we first started using WordPress on our sites - no false positives at all, and comparatively few let through the net - and we've never had any problems. So I've never seen any cause to look for alternatives - which probably explains why, to be honest, I'd never heard of antispambee.
Another vote here for Akismet, although I haven't tried Antispambee. Whilst I will often 'un-spam' comments that Akismet has caught, then edit them before approving them I don't think I have encountered a single comment that it has wrongly reported as spam.
FYI - I had trusted and used Akismet for years and added it on a client's site. A hacker got in through the Akismet plugin, which I found out is a favorite for pharma hackers (Google "akismet plugin hacked"). I next tried Bad Behaviour but it conflicts with so many of my other plugins.
Thank you for starting this Clinton; Antispambee was new to me. After investigating it appears that is what I am going to try next, because it has filter settings (that I can understand!) and can integrate with Project Honey Pot or GASP (java pop-up that says "check this box to confirm you are not a spammer") if needed.
I've been using Akismet on several of my sites for awhile now without any problems, though its effectiveness seems to ebb and flow over time. Sometimes (most of the time, in fact) it will work great and then I'll have a spate of bad comments get through.
Kharrison's comments on a potential Akismet hack does give me a little concern. I'm hoping the fact that it's so frequently updated should close those holes?
Oddly enough, I still use Spam Karma on a couple of older sites, though it is no longer updated. I've been meaning to move those over to Akismet, but since it's still been working I haven't bothered. I do imagine, though, leaving old plug-ins operating on a site is an invitation for trouble. I hadn't heard of antispambee, so maybe I'll give it a try on one of those.