Schrottie has updated his website that compares the features of the various cache listing services.
Sites included are:
GC - Geocaching.com (basic)
GC - Geocaching.com (premium)
OC - OpenCaching (v 2.0) (de, it, others) (doesn't seem to have ANY features not in 1.0)
OC - OpenCaching (v 1.0) (pl, us, others) (actually seems to contain features NOT in 2.0)
AU - Geocaching.com.AU
OX - Garmin's OpenCaching.COM
TC - TerraCaching (basic)
TC - TerraCaching (premium)
Interestingly, even though I believe he is from Germany, where Navicache seems to be most active, it is not included.
Brief summary of the site:
This comparison is based on the features that the respective platforms offer to the user. Only those functions that serve the purpose of using the data have been evaluated. The quantity and quality of the caches have not been evaluated because they are user-generated content and cannot be influenced by the platform operator.
For geocaching.com, basic and premium membership are listed separately because there are many differences between them. In the original Opencaching, there is a distinction between old and new code base. The old one is in use at opencaching.pl, opencaching.us, and at other nodes. The new code base is in use at opencaching.de and opencaching.it, among others. Opencaching.com has nothing to do with the free opencaching network; why Garmin as a (commercial) operator still chose this name, will probably forever remain a mystery.