I've been designing and developing with Wordpress for about two years (and I love it). Recently, a respectable designer told me that I could work for him. He works with Joomla! My job was to create a Joomla! template. I didn't feel myself comfortable using it. I don't like the back-end's UI, the way you add elements and content (I don't even like Joomla!'s logo). I'm used to simple interfaces and Joomla! seems too cluttered to me.
That's why I started to wonder if I'm better off just finding clients and using the CMS that I love or making an effort to learn a CMS that I don't like using?