I received a message from a reader in Germany pointing me to a very comprehensive list comparing various geocache listing sites. Garmin’s opencaching.com site is not yet listed. We will have to wait for an updated list in the future. The site is in German and can be found here: http://dafb-o.de/oc/plattformen/vergleich.html
Follow this link for the English Translation provided by Google of the Geocache Listing Site Comparison.
Here is a screen capture of a small portion of the comparison. This is a great resource. Maik Bischoff, the author of the comparison, told me that he will be creating a revised English version in the new year.
Thank you to Waldemar for bringing this information to my attention.