It really comes down to whether it contains vodka or tequila. Tequila is a Mexican distilled drink that comes from the agave plant. It has a stronger taste than the milder tasting vodka, therefore it changes the flavor profile of the drink enough to need its own name. The remaining ingredients are up for interpretation, based on preferences, but generally speaking a Bloody Maria tends to be spicier and include a higher number of spicy ingredients that give it a kick!