Well, Silo isn't free, but it's reasonably priced. I just happened to get it in a good sale last year. I find it's UI clean and easy to get around in.
Blender IS free, and I've been using it for many, many versions, long before the current UI debuted with version 2.52, and I find this UI much easier to work with than the old, unprofessional looking UI. Of course, since as you mentioned, I've been using it for years, so I'm used to it. It does have a learning curve, but there are hundreds, if not thousands, of tutorials on YouTube, as well as several Blender related forums, which can help you learn to use it. Check out the long list of Blender resources I set up in the Blender forum here to give you some kind of idea.
I haven't used ZBrush much, and what I did do with it (created a Samurai style sword, it wasn't very difficult, but I was following a tutorial step by step as I worked. I haven't tried creating anything from scratch by myself, as it were.
I also have an educational license for Maya, and even though I've always wanted to play in it for many years, it took 6 long videos just to figure out where everything was in the UI, so I don't even want to think how long it'll take me to learn how to actually create something with it.