S&W Model 25-2 in .45 ACP with barrel shortened to 4".
Or a S&W M27/M28
For semi auto, customized Colt 1911 in .45 ACP tuned for reliability. If we're talking "old school" I take that to mean the ammunition technology available is also "old school", which means I'd pass on 9mm. For revolvers it'd be .357 Mag or .45 ACP w/ moon clips, for autos it'd be .45 ACP. In my mind 9mm only became viable with the current newest generation of expanding ammunition technology.