I can do both; sometimes I sip, other times I drink it more rapidly. It usually depends how thirsty I actually am. Coffee is something I've considered, I just haven't acquired a taste for it yet. Try as I might, I can't drink more than half a cup. I actually can't stand diet soda either, it just tastes weird to me. I also drink some non-carbonated caffeine filled drinks, but those also have sugar, and I just can't get into the habit of drinking anything that has caffeine but no sugar.
Part of it definitely is an unconscious habit, though. I'm fully aware that I sometimes just drink whatever I have with me without really tasting it.