Despite all the naysayers, there's no medical evidence that cola drinks, with aspartame, are harmful, provided one doesn't drink dozens of them over a prolonged period.

Coffee isn't horrible if consumed in moderation.

Socially, an active LDS person has a problem drinking coffee. However, we had a leader who regularly drank decaffeinated coffee, so there's that.

Personally, I love Diet Coke and loathe the taste of coffee. So it's an easy one.