Analytics, no question. I've only recently discovered just how bad alexa is. One of my sites - approx 500 unique visitors a day - Top 100K (~92,000) Another of mine - approx 2,000 unique visitors a day - 600K rank
Here's a list of 50 tracking methods for websites. I haven't looked at them all yet, so I make no claims for how well they function. http://mashable.com/2009/01/12/track-online-traffic/