If you're looking for accurate, affordable site stats and traffic indicators, there are a lot of options available.  In fact, it seems like new stats and usage numbers come out almost weekly… each from a different source.  And while they're usually similar, none of them are really consistent.  Even here at the Internet Marketing Monitor.  We've got a couple of tracking solutions installed and get different numbers (sometimes wildly different) from each one.

So which one(s) do you use?  I ran across an excellent overview of the topic at Traffick called "On Alexa, Compete.com, Quantcast, et al."  It looks at, obviously, Alexa, Compete.com, Quantcast, Google, Yahoo, Technorati, and other sources of usage information.  And while it isn't a comparison, per say, the article does raise some interesting points about all of these services.

Citing numerous reviews and comparisons, the author makes the following assertion: 

So: some services that aren't really intended to be traffic measurement services predict actual traffic far better than those who make this claim for themselves, it appears. And Compete.com, in SEOmoz's study, comes in below Alexa, which doesn't fare too well in its own right. Shouldn't our cheerleading, then, be directed at Technorati and Yahoo for their fine free tools, and not mysterious startups who have yet to show us anything concrete?

To a degree, he's right.  But I think the main thing I walked away from this article with was a reinforcement of my existing opinion:  no one source of statistics is going to provide the perfect picture (which the Traffick article also says, by the way).  Hitwise collects data this way… Compete.com collects data that way… and your own server collects data another way.  The means are all different, even though the end result is supposed to be the same.

The original question was "which one(s) do you use"… and I think the best answer is simply "all of them".  One of these services is going to catch something another one misses.  One of them is going to highlight something that another one buries.  You're going to notice something in a report from Compete that you missed in a report from Yahoo.  So the best advice is to combine them all into a "master record", if you will.

For "official" reporting purposes you'll choose one way to collect information.  But for your own personal benefit, combing as many sets of data as possible will produce a much broader picture than one or two services alone.  And when people ask about your numbers, give them a range… or an average… and explain what you mean.  With the experience of gathering data from all of these services under your belt you'll not only understand the strengths and weakness of each service better, but you'll be able to explain how they affect you and your site.

More information is usually better than not enough.  And each of these services has something to offer.