Timely post as I was looking at both of these lights as well... I previously picked up the RRT-1 and, while it was beautifully made, I couldn't find much use for it. I sold that light and decided that I would like to own another JetBeam as I have had, at one point or orther, 4 JetBeams. :naughty: So, between the RRT-0 and Jet I v3.0, I chose the Jet I which I just purchased 2 days ago.
The reasons, as stated by some, are: the clip, 3 programmable modes and ability to use either 14500 or AA without switching tubes. These three clinched it for me. I do like the look of the RRT-0 with the ring selector as well as its ability to fit the AA tube but, in actual use, I decided that I would really have to make a conscious decision to use either R123 or AA as I would not carry a spare tube with me.
Good luck with your choice and let us know what you decide and why.