The 12 gage or 20 gage?

I was out for my first dove hunt this week with my German shorthair named Finn. When I was loading the truck I couldn't make up my mind on what shotgun I should bring along for the hunt. The 12gage or 20 gage? This sparked the idea on shotgun choice. Here is a knowledgeable Sportsman Warehouse Sales associates with his thoughts on shotgun choice. Sportsman Warehouse has a huge selection of shotguns to choose from. If I were new to the sport of upland bird hunting and I was in the market for a very affordable shotgun that can do it all, what would you recommend and what would that cost?