I have used 9x21,38 superauto,38sp& 357 mag,44 sp&mag,45 Acp,45autorim,and 45lc,in revolvers,leverguns and autopistols and semiauto rifles.
I love them all,all of them,they shoot better than I can hold.
In my neck of the woods,I am the man to beat at 25 and 50 meters ,from offhand,standing with a couple of marlin cowboys in357 and 45LC and placed honourably at a pin shoot with a 911 45 HP with compensator.
I can shoot comfortabily and well from a 911 autopistol with 200 powe factor loads,while I tolerate much lesser recoil from my S&W DA revolvers.
I have a peacemaker clone in 44sp that shoots splendidly,and at point of aim with 750fps 250 grainers.A n immense blackhawk bisley in 45lc I found painful to shoot.
A 9x21 browning hp with 950fps loads(as in Ed Harris'articles in handloader and the FS) is reliable but not phenomenally accurate,
I would say that the gun is the first thing to consider,No single caliber is inherently more accurate,but that some caliber are easier to shoot and reload for.The reason are, brass quality,bullet and moulds availability and the pressure at which they work.
I would give my vote to the 38-357 combo,close second the 45ACP-AUTORIM And do not forget,the 44sp(,I am waiting for a 44mag marlin lever action),though 44 mags in lever action or contender have a queer chamber, 1/10 of an inch longer than the case.
And what to say about a 45 long colt cowboy marlin,it shoots splendidly 300 grains bullets at 45/70 speeds.
Please,forgive me,I cannot make a choice,I love them all.
I fear that other older calibers in bottle neck cartridges are a mess to load,and what about the 41mag? He should have been born before the 44 mag......
Pistol calbers that do not pierce my ears or hurt my hand are like an illness ,a bug,an addiction to me.And if Italian gun control laws did not restrict my arsenal,I would surely follow Ed Harris in his stugy of 32 revolvers or 32ACPpistols,not to mention the mauser 96 pistol and............someone hold me!........
When my spanel bitch gave birth to four cubs We were unable to sell them,only gave a she dog to my daughter and it made my heart bleed.I kept the other three ,with their parents.So it for me with pistols,I would love to have them all,every caliber and type of gun has his po and con.