Half a pint to a pint will be fine. I used to put them in a huge mug and add hot water for a lovely hot chocolate before bed also nice with a spoonful of coffee, like a mocha. Or for this weather you could put in a pint glass add some cold water and crushed ice.
Everyone's tastes are different. I personally found them quite rich and although I would drink them from the carton at work, at home I preferred them diluted a little bit, didnt have to worry about glugging the extra water that way either
You are right, everyones tastes are very different. I hate the Tetra's watered down. I like the chocolate Tetra in an emergency or when I have had 2 packs and I feel full and don't really fancy my third, but I find they don't fill me as much as a soup or a shake.