I mainly code ColdFusion or PHP (and JS/CSS/xHTML), but have dabbled in a bit of RoR. RadRails/Apatana has been great for me, because it's built on Eclipse, which I was already using for my other work. It also integrates with Subversion via the Subclipse plugin.
The Eclipse platform is so extensible that it's worth investing a bit of time in to learn, but then again I like having a single IDE rather than having to switch between different apps.
I briefly looked at Netbeans, but TBH Eclipse just felt better for me, and Aptana itself is great when you come to do anything in JavaScript.
YMMV...
