Which is your operating system ?

• On Mac, there s Textmate. For ruby or any other development, it s a dream to use.
• On Linux and Windows, there s both Netbeans and Aptana.
  I don t know for Netbeans. But Aptana has a quite good support of rails development with the Radrails plugin.

I really like Sublime Text 2. It is a lot like Textmate, but it is cross-platform so you can share all your common workflows and snippets (or other collateral) with your team regardless of their platform.

It also has a really cool "minimap" feature that shows multiple pages of code in a little sidebar. This image is from their website, showing the minimap on the left of each screen. You can click anywhere in the minimap to jump to that part of the code, so it s not just great for visibility of the whole code set, but as a nav tool too.

RubyMine gets a lot of press and runs on windows. It s free for open source and classroom use. I d say it s probably better than Aptana or Netbeans, but I use TextMate fulltime and haven t revisited it in a while.

gVim if in Windows or Linux.

textmate if in OSX

Otherwise gVim

Notepad++ hat also Ruby syntax highlighting

• Mac : textmate
• Windows : e-texteditor, sublimetext
• works everywhere (and linux) : rubymine, aptana, vi, emacs, netbeans

EDIT: I m now using Sublime Text 2, it works on all platform (but is not free)

I d like to throw gedit in as well - It s what I use when I develop with Ubuntu. You can find a Windows version of gedit here.

NetBeans is heavy (full IDE compared with a text editor) as mentioned, but it s free and it works pretty well.

• cygwin and vim

I ve tried the various IDEs as well as e-texteditor, but they re all pretty painful to me. Emacs, on the other hand, is much lighter-weight and is available on all the various OSs mentioned (yes, the OP is on Windows, but other folks have been bringing up Mac and Linux).

My officemate (who was pretty die-hard about IDE use) just switched to VIM for Rails development on Linux because RubyMine (the best of the lot) was too buggy under X.

use Vim(+macro)

I would suggest ATOM from github. Works like charm. Have been using it for developing Rails app and loved it.

I wrote a lot of Ruby code on a daily basis. The best editor, in my opinion ( and for Windows/Linux ) is Komodo Edit. Notepad++ doesn t have great autocompletion, RubyMine is too slow ( and not that great ) and Netbeans/Aptana are too heavy.

The only downside ( if you care ), is that it takes a bit more for the startup. After that, it runs great.