Personally, I think that top and vmstat are a bit low on the list; they're typically the first things that I run. While they're too general to provide good troubleshooting of the actual problem, they do a great job of pointing out to me where the problem probably is.

User experience reports are nice, but rarely indicate something other than "load is high", or "server is unresponsive". vmstat and top not only can tell you that, they can start telling you why and where to look for your problem.