SpamTitan filters out more of the spam, with less false positives that the product we used to use. It has a better interface which is very easy to use as well. I haven't found anything to dislike yet.
I would recommend a serious potential user ask for a demo. You can sort of see right off that it is a powerful setup.
Before using SpamTitan I basically had to blanket block most countries outside of the US. I also had to deal with frequent complaints from staff on the amount of spam getting through. Now I have only 2 non US domains blocked, and get maybe 1 concerned staff email a month. I love this product!