Vlad is another good Capistrano alternative written on top of Rake. http://rubyhitsquad.com/Vlad_the_Deployer.html

I used Vlad for a while and liked it okay. It's a bit simpler (using 'real' ssh instead of net-ssh, and rake for running tasks instead of its own thing).

I ended up going back to Capistrano for git submodule support.

They're pretty interchangeable from a user perspective. I just use Capistrano everywhere now.

I am using http://labs.peritor.com/webistrano to deploy my php stuff. It is capistrano + UI. I am very happy with it.

I think Capistrano is so good that I never consider making a change. Should I?

Not if you're happy with it!