Choosing A or B locks out one of the characters for play in story mode after the last mission, that's why. Online mode is great when you join a crew and start earning cash in jobs... you can buy cars and save them in your huge garage, fly jets and helos just like story mode, arm wrestle, steal specific cars for cash, and more. PLUS, you can create female characters, which is a blast... I'm Foxy Brown LMAO