I haven't tried Webtrends personally. From what I've heard it's extremely detailed, but very slow to generate and only creates static website reports.
I'm looking very seriously
at Mach5 FastStats Analyzer Gold because of its interactive analysis capabilities. Its only downside is that it's utterly inept at geographical analysis (though I know a way that could be improved, I'll contact the authors and see if they'll implement it). Everything else about it is superb. Once you've tried FastStats' HyperTree View for tracking visitor paths through a website, you realise no static reports could ever match that.
I'm using it to filter out superfluous stats
(ie filtering out specific HTTP error codes), track search engine keywords to specific sections and files on my site, and to determine return on investment from online ads and referring sites to my e-commerce site. $200 is a sizeable chunk of my revenue, but I think it will be worth it in the long run.
PS FQs stats have satisfied my needs for the first four years of my site, including 2 years of e-commerce.
PPS Cheers to Andi for suggesting Mach5 to me, once again you've come up with goods!