Cornerstone made a dashing premier as a full release recently, outpacing the much-anticipated Versions in its development cycle and leaving many of us wondering: why couldn't we have had such polished Subversion clients back when Subversion really mattered? With friendlier and more flexible version control systems like Mercurial and (my recent favorite) Git taking center stage, it just seems odd that two applications devoted to last year's RCS are vying for the spotlight.
After a 10 minute tryout, I have to say that Versions, though still in beta, was more intuitive in general. I really, really like the timeline feature in Cornerstone, though, which allows you to Command-click any two points on the timeline and see a diff with the built-in viewer. For basic Subversion-related tasks (and probably more advanced tasks that I didn't delve into yet), both clients are far ahead of what currently exists, both in usability and aesthetics.
For those who still have a strong interest in Subversion, and who haven't already sworn allegiance to Versions at some point in the year (plus) we've been waiting for it, Cornerstone just crowded the playing field. You can read more on Cornerstone at the Zennaware website.
Addendum: As noted in the comments, my impression that Subversion is being relegated to obscurity (and the bias which that impression created in this article) is entirely without basis. I concede and would like to say that, given the stats, it's great to see some clients with real polish coming out.