First I should make it clear that I work for WANdisco, the company behind uberSVN.
I'm not aware of a comparison document for the products mentioned (though if anyone wants to write one I'd be happy to help).
When it comes to uberSVN and Collabnet Edge you'll find a lot of similarities in terms of functionality. With the exception of a few features it's likely to be a matter of personal taste as Mark said.
We've done a lot of work on the UI to try and make it as simple and slick as possible, so hopefully there's not much missing there (if there is I'm happy to take feedback on that). Note to @David W, Edge has a web front end now too.
Feature-wise uberSVN has more in-depth LDAP and authorisation features. You also get svn:// support, the ability to switch between Subversion 1.6.x and 1.7.x, and the ability to set DAV location. There are a few paid apps also that add a whole range of ALM features to uberSVN as required, without having to install an entire new product (with Edge I think there comes a point when you have to go down the Teamforge route for certain things).
There are a couple of features that Edge has that uberSVN doesn't yet, like the ability to add multiple repo's at once and automated scheduled backups.
Edge is also the only open-source product of the three, though we are planning to release an SDK at some point in the near(ish) future which will go some way to increasing the customisability of uberSVN.
VisualSVN suffers for me in that you don't have remote admin in the free version, and the fact that it's Windows only. Again though, if those aren't an issue for you it comes right back down to personal taste.