Surfingkeys has a couple of features over cVim that I really like:
-pressing '?' on any page will open the list of shortcuts
-searching through bookmarks / history ('t') is prettier
-very useful feature of switching through all the current open tabs with link hints ('T')
There's one shortcoming I noticed, however, is that when you go to the link hint mode, there are no indication than you entered it. On cVim there's a "follow link" notice in the lower right corner.
I'm a fairly casual user though, someone else will probably find more differences and pros / cons for each extension
I've tried a bunch of these "vim-like" plugins and I always come back to Vimium (on Chrome). On Firefox I'm stuck with Vimperator, which means I don't use Firefox very often.
Why so? Firefox is still my browser du jour mainly because of Vimperator. I also use Vimium when in chrome, but Vimperator is way more powerful, and plugins are trivial to write: https://vimpr.github.io/plugins-en.html
Now how do they compare?