What are the differences between rbenv, rvm, and chruby?

I'm new-ish to Ruby and Rails. I am looking for a purely objective list of features and advantages/disadvantages of each. In an effort to keep preference out of this, please refrain from answering unless you have used all 3 systems.

There's three main options available today:

• rvm which is the most established, but also the most intrusive in terms of shell modifications.
• rbenv which is lower impact, and still works as well.
• chruby which purports to be even lighter than rbenv.

Personally I prefer rbenv because it works well with Homebrew and doesn't mangle the shell environment as much, but tend to use rvm on servers where that doesn't matter because they're set up for a very specific purpose.