Just a matter of individual taste. I love the taste of Khaos. Mixxxer is good too - its a grape/apple juice based Monster. You have any bulk food stores in the area? There's one around me that carries cases of various energy drinks. Might try looking there or some smaller party stores or something.
Edit: You could also buy them from
Thinkgeek. I think they still do the recurring delivery, so you can have them constantly shipped to you on a regular basis.