If I were a working LE officer; plainclothes/soft clothes investigations or a sworn federal special agent, I'd pack a HK P2000 LEM in .357sig with night sights with a smaller DA/SA P2000sk .357sig as a BUG-2nd gun.
In cold weather or in some conditions I may use a SIG P220R DAK .45acp with a Ruger LCR .357magnum, a S&W 642 .38spl or a .44spl Charter Arms Pug(DA only) as a back up.
In general, I'd use either the .357sig or .40 for LE duty but I'd carry other sidearms depending on the uses(raids-warrant service, stake-outs, PSD/protection details, etc).
Smart badge-packers use a 2nd gun or back up that can take the same full size duty magazine or they carry 2 pistols AKA New York Reload.
Clyde