Soda
My dad was always a soda dinker --"pop" to him--and so I've been exposed to it as "normal" as long as I can remember. I also share his love of certain comfort sweets so I think i inherited his sweet tooth or something. I like it for the taste (and so really have my preferences) rather than the caffeine, though both it and sugar are addictive.
Not sure if I ever really "quit," though I stopped buying it for home a couple times and have had withdrawal headaches several times when I convince myself I don't want it for that month or whatever. Other people would just buy it for me (roommates, my sister or mom when they'd come bother me, etc) or I would get it when out i.e. restaurants, while shopping, pick up a bottle from the gas station when driving, machines at work.
In college I was drinking it constantly, partly because I can't stand alcohol and partly because caffeine really helped with constant 3 hour nights between work and being a gaming nerd going to game school. After that I started trying pretty hard to hop to water with that flavorant acid crap (Mio or whatever) and I still do drink a lot of bottled water, but never succeeded in cutting all the soda out.
These days I drink a can or two a day. 12pack goes about a week, generally have one mid-day and then one winding down for the night (I know that sounds counter-intuitive). Funnily enough, I can't do energy drinks (and not just because they are nasty). I had half an Amp once and I was jittering uncontrollably for about an hour. It spooked the hell outta me, especially since my job at the time was operating heavy machinery in close proximity to other people.
My step-dad used to drink it instead of coffee in the morning. I'm not a morning-anything person, but since I despise coffee I imagine I would do that if sweet stuff didn't make me nauseous after waking up.