I recently tried a spam-fighting experiment. I thought that having Bad Behavior & SpamKarma2 running simultaneously might be slowing down my site, so I installed Akismet alone.
But the result has been a dramatic rise of spam that has escaped Akismet. Before I got almost no spam that I had to moderate. Now I get 20 or so spam comments/wk. that escape the filter.
I wonder whether people use Akismet alone & find a diff. result; or whether most people use Akismet together w. either SK2 or Bad Behavior.