BayesIT came as part of the installation package when I first tried TB, but I found it a bit lacking. Then I tried the AntiSpam Sniper plug-in and it works quite well for me. Like all Bayes filters, it requires training. I used a sample of about 400 saved spam messages initially, together with a smattering of my saved good messages, and it's currently doing better than 97% accuracy. The errors are mostly failure to detect some of the newest image-based tricks of the spammers, but occasionally it puts a good message into the junk folder, so I still scan over the folder before blowing its content away.
Features of the Sniper that I like, and have not found in the other plug-ins I tried, include a "friends" list of addresses that won't be filtered at all, which I can edit at any time; a black-words list that can help identify spam without need to do more than parse the Subject line of the message; black rules; and white rules. The friends list can be built automatically when you flag a message as "not junk" or can be done by hand.
All in all, it compares quite well with PopFile which I used with my previous mail client, and unlike PopFile does not seem to be prone to freezing up at unpredictable times. There's a free version that doesn't have all the features, but the paid version is quite reasonable in price, and the developer is quite responsive to questions...