Webdav is really one of the really ugly design decisions of the Subversion project. WebDAV was initially promoted by Rational - if you closely study WebDAV, it is easy to notice similarities with Clearcase. Looks like it was a political choice that was made to appeal to the managers in the IT departments - "Oh, Firewalls are not a problem, If your browser works, then the SVN should work ... blah blah". To be fair though some of the top committers will freely confess to a dislike for WebDAV.
I always use svn+ssh. I had it under HTTPS initially (first using Apache, then Lighttpd), but it had a strong tendency to corrupt the working copy. Like daily. So I had to go in and delete .wcprops after every substantive check-in, which got really old really fast.
