My choice was based on a few factors - the license fee had to be reasonable, the app had to have built-in side-by-side diff functionality, it had to support multiple repositories and it had to have a nice clean user interface. Cornerstone meets all of these for me.
The only downside I found is if you have large commits (100+) files at a time, Cornerstone does tend to crash if you commit from the main window. However, right clicking your working copy and committing from there works just fine.
Here are some screenshots (with my work related repositories and working copies edited out).
This is in no way a full review of the app, just my personal opinion after experimenting with a number of different SVN clients.