I don't have a comprehensive analysis, just a general feeling. I really like coding Rails apps using the NetBeans 6.0 Milestone. I love Eclipse, and switch between the IDE's depending on the specific task, so this is not coming from a particular camp.
I like RadRails a lot, but it seems to have stalled a bit. I kept having problems where the IDE would loose my Rake tasks. I found a fix to manually add an Eclipse builder to the project, point it at rake, etc. Even so, I still periodically see the app forget about Rake. A small complaint, really, but it frustrated me enough to switch. What I found in NetBeans is a rather tight-feeling, smooth IDE for Ruby on Rails. No big analysis, just a nice experience. I'm back to coding, and my IDE seems to not forget about rake. Now if only I can remember my anniversary coming up!