For most of 2008 I used WordPress.com Stats (averaging about 75 "views" per day) and this year I'm adding Cystats to the mix.
Based on my early experience (16 hours), the Cystats' numbers appear to be much higher (and much more detailed, of course). For example, Cystats is currently showing 234 "unique visits" (without bots) since I implemented it shortly after midnight and WordPress.com Stats is reporting 17 "views" since last night at 7:00 pm.
Is it a difference in what they are reporting or are they really that far apart? Which numbers are more reliable?
BTW, I just changed the setting to not include my visits in Cystats so some of those early visits are mine, but there weren't that many.
FWIW, I like Cystats numbers much better! :-)