With rails changing so fast does any IDE on the market, open source or retail keep up with all the changes. So many are still setup for rails version 2 that when you setup your development workstation they choke.
The snarky answer is textmate / submlime 2 / vim.<p>I'm no rails guru, but I have but together quite a few professional CMS's and use it almost exclusively for homebrew projects, and I've never felt like I needed a heavyweight IDE.
Was using Netbeans and then RubyMine when I first started. Then sat down one day for twenty minutes to try:<p><pre><code> $ vimtutor
</code></pre>
Never looked back. It's been six months since I started Vim and I realized all I really want to develop Rails is a fast way to switch between files, find files, and arrange files onscreen.<p>The CommandT plugin for Vim has been absolutely amazing. You just start typing the path of a file and it'll narrow down search results. For instance if you want to get at a controller app/controllers/posts_controller.rb, you can just type any letters along the path. like, i'd type "acposts".
I prefer Netbeans with Ruby-Rails plugin. Allows me great code navigation, visual debugging and also can be made to highlight SASS/CS via plugins, good support for html/css, auto-formatting of code.