I will have to say all five have been reliable. I have a couple of Colt Pocket Nines which have both been reliable. I also had 2 R9's, the current one is 100% with whatever I have fired in it and the first was complete junk and went back to Long Island for good.
The R9 is the lightest and with the shape of the slide is easily the most concealable. That is why I puchased it. I have no problem pocket carrying any of them, so I go with the one "I can shoot the most accurately with the most speed". With my stiff and arthritic hands and wrists I have found it hard for me to get 7 shots off as fast and accurately with the R9 as I can with the PM9, Solo, and the Boberg.
I am still testing the Boberg which is by far the easiest to shoot and may end up being my first choice but for now, I prefer the Solo.
Remember, Carry Weapons are meant to be comforting, not comfortable.