Over on the garagejournal.com this comes up regularly, this seems to be the general consensus amongst the folks there:
Milwaukee gets props for power, size, and battery life
Dewalt gets props for power, battery life
Ridgid gets big props for the warranty
I settled on Dewalt years ago, I have a bunch of old 18V tools that I use the 20V adapter on. My favorite for everyday use is the Dewalt 12V driver, drill, and impact. They are light and very powerful, it is pretty rare that I break out the 18v hammer drill with the 20v adapter, it seems huge.
My youngest Son went budget on me and bought a Ryobi set. He was happy with it at first, then went to work for a Division of Stanley/Black and Decker. Once he got his hands on the Dewalt tools he was very unhappy with the Ryobi in many ways, including the dead batteries, and sorry he spent his money on them.
This is one of those discussions that can be very polarizing, folks like what they like, if I had to start new, I would take a serious look at Milwaukee before I went yellow or orange.