Recently (few months ago) I've switched from RubyMine (around €90) to VIM (exactly €0) and I'm really happy with that.
It's not easy to describe why it's better but one thing I love about VIM is that I don't need mouse anymore. It probably sounds funny but I feel much happier without a mouse - because it frees me from the table.
In VIM you'll find helluva lot of nice features - just google around. For example one of the best is ci"
which will delete all text inside "
and you can start writing. But there are many many others.
The full blown IDE's are IMHO useless for Ruby and other dynamic languages. Their best features like: refactoring, code completition, syntax checking, etc. simply doesn't work. Or worst - works on 80% percent. And they will never work as Rails are full of eval(some_text_that_generates_methods)
I can't speak for Emacs as I've never used it.
I'm not sure how is it on Windows platform as I'm on Mac/Linux. But it should be similar.
UPDATE: Ah, I forgot to provide a link to nice VIM setup for Ruby on Rails: http://github.com/akitaonrails/vimfiles
If you follow the README you will have a working environment ready in a minute. There are many useful plugins in this repository (git submodules to be exact) - just take a look inside.