I basically look at it as a compromise between control, portability, utility, power and concealability, and legality.
If Concealability is not an issue at all, but the most effective weapon is needed, as in home defense, well I reach for a rifle, if I want greater utility and power, and range/rapid followup shots are not needed, a shotgun is ideal. And in many places a "truck gun" is legal, but CC or even posessing a pistol is not.
If I need a weapon that keeps my hands free, can be drawn and fired quickly, is very portable, but needs for concealment and power are minimal, as a law enforcement officer would need most of the time, well then a full size pistol is ideal. G17,g22, beretta 92, 1911 duty calibers 9mm, 40, 45 10mm in autos, 357mag, 41mag, 44sp for revolvers
For a weapon that takes little effort to effectively conceal, but retains most of the power, capacity and control of a full size, then the compact or midsize pistol is best. G19, g26, hk2000, m&p compact in duty calibers, 9,40,45 for autos, 38+p, 357mag for revolvers
For absolute concealability and portability, where power, capacity and control are even less of a neccesity, or a backup to a main weapon is needed, then the mouseguns or pocketpistols come into play. ppk, p3at 32acp or 380 in autos, 32h&r or 38sp in revolvers
Different needs require different tools, there is alwas a level of compromise that must be reached in order to be comfortable with your choice, and physique makes adifference too. Someone who is 6'5" 300lbs and wears baggy layered clothing can probably hide a 6" 1911, or a HK mk23 without much effort, and might find anything smaller than a fullsize uncomfortable, or uncontrollable. A 5' 90lb woman might be able to get a full grip on a G26 or ppk, and be quite comfortable with a lighter and softer recoiling pistol, but anything larger would be uncomfortable or impossible to conceal. Basically there are so many choices one is bound to fit within the needs of most.