You should try all the RoR and settle on the one you like best.
First you should check out Marshall Vandegrift's excellent screencast using ECB, ruby-mode, emacs-rails, and some other stuff. It gives you a good feel for how cool writing RoR on Emacs can be.
In short here are some of the modes you should try:
- Rinari - A simple framework for getting around your code, running tests, and managing consoles, web-servers, etc. It's minimalistic and revolves around a series of key-bindings.
- Emacs-rails - the grandfather of Emacs RoR modes. It hasn't been updated in a while, and in fact the primary homepage no longer exists. But it's quite powerful and lets you do almost everything.
- Emacs-rails-reloaded - This is a re-design of the original emacs-rails, I believe by the same guy. It uses the the great anything mode to help you find things and get around. I am using this AND rinari currently.
Here are some other modes that are useful:
- ECB - the Emacs Code Browser. Use it for project management, and getting around your code.
- Yasnippet - provides all kinds of useful snippets, automatically inserted with the TAB key.
- Nxhtml - For editing rhtml, erb, etc.
More modes you might try:
- Ri - for viewing ri documentation inline.
- Flymake-ruby - on the fly syntax checking.
- Ri - for viewing ri documentation
Oh and of course you need ruby-mode, which comes with the ruby source, and is maintained by Matz himself.
Hope this helps