The only one for me is Tesco's "Kick"....OK, it tastes like p1$$, looks like p1$$, and probably IS p1$$, but it's cheap! With my shift pattern and permanently suffering from jet-lag, I get through 3 or 4 LITRES a week.
If I could find a way to hook up to a continuous intravenous supply of pure caffeine, I would probably go for that instead.
[scary thought time] FYI, at least 85% of coach drivers that dont do regular (ie: school) runs are the same. [/scary thought time]