Congrats, and a big sweeping 'tip of the hat' to you, Citizen!!!!
Also THANK YOU! for your service, Marine! Carry on.
Choice of firearm? Depends on YOUR feelings....
Like the "Old West" era? Single-Action revolver & Lever-Action rifle, maybe double-barrel "Coach Gun"
WWI/WWII/Korean War era? 1903 Springfield rifle, or the US Rifle Cal .30 M1..."The Garand" ans same selections as a tribute to the men that stormed the Normandie Beaches on D-Day
Vietnam & Later? M1A (M-14) or the AR-15 type.