...an easier poll than trying to estimate comet impact craters...
Hard to believe, but it's one year since Cassini arrived at Saturn.
On JPL's Cassini website (which I sadly admit to visiting every day since Cassini arrived), they're celebrating by conducting a poll as to what is the favourite image (...thus far - we're only one year into a very long mission).
http://saturn.jpl.nasa.gov/multimedia/poll/index.cfm
Visit the website. Cast your vote, but hurry before they announce the results. Then come back here and tell us why.