Coffee. Hands down.
I have been drinking coffee every day since I was 11. My parents never drank it, but we always kept some around for company. One morning I just felt like trying it, so I made some and liked it. End of story. I am so addicted that I can't function without it. I am, however, back down to 24 oz per day. It's weird, I've been drinking it for so long and become so dependent, that I've kind of gone the other way: one travel mug's worth is enough, and I just don't want any more after that. It's very strange.
That said, if by some chance I have more, I don't really feel a reaction. Coffee no longer gives me a "buzz." I just enjoy the taste and as long as I have a certain amount of caffeine in my system, I'm good to go. Strangely, delivering the caffeine via soda or tea or something else doesn't do it. It HAS to be coffee, which leads me to believe that my dependence is to a certain degree psychological.
While I prefer good coffee, and I prefer it strong (I can enjoy it black but IMO if you can drink it without milk it's not strong enough), I will say (shamefully) that if desperate I will drink whatever kind of coffee I can get; even if from the gas station, or re-microwaved leftovers from yesterday's pot (sometimes in my desperation, the microwaving is an extra step that takes too long, and I just drink it cold). I'm none too happy about it when it happens, but shitty coffee is better than no coffee. In general, however, I find I go to great lengths to ensure that I maintain a high level of quality for my coffee consumption: picking my beans with care, grinding them fresh, measuring carefully, using spring water, etc.
And dark roast? Bah. The darker the roast, the less caffeine it has. There is a cafe near here that has a drink called the "White Tiger" which I have had ONCE. It scared me to death, I felt like I'd done a line of coke. Honestly I didn't feel like I had a good handle on my reality after drinking it. It's basically barely-roasted coffee beans, so the caffeine concentration is *extremely* high, and then they brew them espresso style (a double shot) and top it off with steamed milk. It's quite tasty, but very frightening.
I drink tea to relax. So in general when I do tea it's of the herbal variety (chamomile or rooibos) to make me sleepy before bed. I used to do formal tea parties with my girlfriends every spring, with high-quality bulk teas from a local purveyor, little sandwiches, hats and gloves, the whole bit, but recent Circumstances have thrown a wrench in that in recent years.
As to the microbes that make our life better... cheese, beer, kraut, wine... these things are delicious affirmations of life, and should not be judged because of their smell or their association with bacteria. Bravo, yogurt! Bravo, kefir! Hallelujah mead!
I'm a little nervous about trying kim chee though.
And I absolutely draw the line at that crazy Corsican maggot cheese.