Of course, Pepsi-chan would be the main girl and a Tsundere type.
All the other sodas would be more interesting, but Pepsi-chan would have more general appeal.
Coke would be an older sister type and would be of drinking age and a bit of a lush.
Coke has a younger sister who bounces from one fad diet to another and frets about her weight all the time. She also eats constantly, but it all goes to her chest.
Mt. Dew would be an otaku gamer type. Her fingers are permanently dyed orange.
Dr. Pepper would be a mad scientist genius type.
Ramune would be OP's incredibly thirsty cousins. OP has 37 cousins, but the main cousin is a traditional country girl who loves summer with green and yellow hair.