Personally, I'd say cans if you can keep them in a cooler and 2L if you have to keep them out so you can put them in plastic cups with ice. If you have to use cups or plan to use cups, use 2L b/c you waste so much with cans where someone pours himself/herself a cup and then forgets about the rest of the can. But if you keep them in coolers, you could just serve cans and not have to worry about cups at all - just have cans of soda, juice boxes and waters or something.
For parties we usually use 2 liters with ice in an ice bucket and cups. However; if for some reason we do use cans we get the smaller cans rather than the regular sized ones b/c we find that people will put down a can of soda and forget about it and get another one and we were always pouring out SO much. But if we use the smaller cans we barely have to pour any "left" ones out
We used to do cans and everyone got a can for themselves. By the end of the party we had a ton of half empty cans laying around.
Now we buy 2-liters and I put a sharpie right next to the cups so everyone can write their names on the cups. We either buy ice to put into a cooler and then set the drinks up on a table outside, or if it's a smaller party I just set it all up by the refrigerator.
Re: cans or 2 liters
We used to do cans and everyone got a can for themselves. By the end of the party we had a ton of half empty cans laying around.
Now we buy 2-liters and I put a sharpie right next to the cups so everyone can write their names on the cups. We either buy ice to put into a cooler and then set the drinks up on a table outside, or if it's a smaller party I just set it all up by the refrigerator.