For me?
J-frame.
That's just me, though.
I'm an experienced revolver owner & user and can shoot the steel & alloy J-frame guns well enough to feel justified in carrying them as off-duty (and now retirement CCW) weapons.
Not everyone finds J-frame revolvers 'easy' to shoot safely, accurately, controllably and effectively. Even among those who do, some draw the line at finding the steel frame models suitable but not the alloy models. Then there are further differing opinions expressed by users when you consider the Airweights and the Airlites, as well as .357 Magnum to .38 S&W Special models, and even among those using standard pressure .38 Spl loads versus +P loads.
Diminutive semiauto pistols are another situation where differences of opinion and personal experience can vary quite a bit.
I don't like to go any smaller than the G26/27 & CS9 designs, and those models relatively similar in size & weight. Even then, after careful consideration and experience I've found pocket holstered carry methods only work safely and effectively for me when used with a certain number of my jackets & coats. Otherwise I'm much better off using belt carry methods with these, and larger, pistols.
My J-frames allow me a wider range of pocket holster carry possibilities when wearing jackets, coats, jeans, slacks and shorts with either deep pockets or suitably stout cargo-type pockets. I've been able to given presentations and work seminars while unobtrusively carrying a J-frame in my slacks front pocket. Sitting can present a potential comfort issue upon occasion when it comes to the holstered weapon riding either on the thigh or being positioned to the outside of the thigh.
Naturally, there are some compromises to consider when choosing a pocket carry method when it comes to safe and effective Draw & Presentation issues, regardless of the platform design chosen.
Now, rather than make any generalized comments about the reliability of any particular design, I'd instead offer the comment that more often than not, day in and day out, it seems the shooter/user of the semiauto pistol is the more likely cause of many more functioning problems than any particular pistol, with the ammunition being a distant second probable cause of functioning issues. The 'best' diminutive pistol design on the market may not work well for an occasional shooter who can't use proper grip & shooting techniques which might be needed for a smaller platform.
I've handled and used a lot of different size pistols and revolvers. I've seen a lot of folks use a rather large range of various make/model revolvers and semiauto pistols over the years of working training & qualification ranges.
For myself, I've decided the J-frame .38 Spl is the optimal compromise for me, and for my perceived needs.
Other folks can, and have ... and will undoubtedly continue ... to choose whatever they find works 'best' for themselves.
It's all a compromise.
