Those who plied the jungles of VietNam would argue for the shotgun (and how they would argue!!!!!!!).
In Afghanistan or Iraq, . . . the rifle would win out.
In the WW1 trenches, . . . the trench shot gun was thoroughly respected.
On Guadalcanal, . . . the rifle was superior.
It all depends on where one is, . . . but for most purposes in the type of conflict I would imagine I could get into, . . . my Beretta semi auto 12 gauge is my weapon of choice as a long gun, . . . 1911 for shorter purposes.
May God bless,
Dwight