Do any of you have experience with WebTrends, OneStat, Urchin or other similar programs to anaylze and report metrics for content effectivenes, search engine results, conversion rates, marketing promotions, web site ROI, etc.? What web traffic analzyers do you recommend for medium to large corporate sites?

I've heard a little about WebTrends and Urchin but never used them. This topic came up during one of my recent job interviews in a corporate marketing organization and I will appreciate your comments and suggestions.