All that aside, plenty of folks use Alexa as a key reference point for advertising deals, business development, and even fund-raising. Simply put, it was the best available free alternative for web traffic measurement. That's until Compete.com launched their 'Snapshot' function this October. Check it out. Compete runs sampling over 2MM users (including Firefox users ;)) and its results are simply a LOT more accurate. I've been looking at two sites in particular that according to Comscore and Nielsen Netratings have over 2MM uniques. On Alexa, their traffic rank and reach are below 3,000 and 300 respectively. Since Alexa bases their reach number out of a universe of 1MM and knowing that total Internet users equals about 1B, that would equal about 300K uniques... hmm. That doesn't ring true.
On Compete, these sites are measured at between 2MM to 3MM users. The other nice thing about Compete is that they offer actual estimates of users (vs an estimate based out of 1MM user universe). Now, there's a few things I'd like to see improved, such as multiple time ranges and pageview estimates, but the accuracy of Compete vs Alexa has convinced me to switch. Still, I'm going to miss Alexaholic :(