If I had to pick one I would go with my Rupes. Don't get me wrong both machines are great and I try to use both as often as possible but the Rupes is very light, easy to hold, easy to work with, and so smooth.
With my Flex I only use the LC interchangeable BP with the 5' Hybrid pads and I will say that those pads work so well on the machine I can't see using anything else.
I know its not what you asked but I like to give my input as this topic comes up all the time. Bottom line you can't go wrong with either machines.