Here is how I rate the four pocket 9mm's that I own.
Conceal ability (pocket carry) - R9(easily), Solo & PM9(tie), XR9s
Accuracy and shoot ability - XR9, Solo, PM9, R9
Over all - Solo, PM9, XR9s, R9
As far as weight and size, you can do the research off their webs. The PM9 and Solo are very close overall as far as I am concerned. The Boberg has the same length barrel as a Glock 26, but I do not get the big increase in velocity that Boberg advertises over the shorter barrel pistols. He had some bad barrels and I might have one. The Boberg is a fun gun to shoot and has minimum recoil and is very accurate. The "reverse feed action" has not been a problem so far for me.
The CM9 comes at a very attractive price and I have not heard anything bad about them.
Overall the Solo just seems to do everything I want and I like it the best.