I drink my coffee black...no sugar...and I seldom drink it hot. The machines in most of the CS restaurants have drinks in which syrups are added in via the machine. I was told there was no way to get a straight up coffee through them. The machines offer 3 types, latte...which is what I would call unsweetened w/milk only (or some sort of milk product), mocha...which is quite sweet w/a hint of chocolate flavor along with the milk product and lastly, french vanilla...again sweet, hint of vanilla flavor and lightened with the "milk". I wouldn't classify any of these as true "coffee". But if I had to pick one, it would be mocha.
As others have said, the Joffrey's kiosks are the best spots to get a made from scratch coffee drink....the real stuff....or as close as you are possibly going to get in the world. That's what I typically go for when I want a coffee when at WDW. You can find a Joffrey's kiosk by looking for their signs that simply say "Espresso Coffee and Pastries". There are none within the Magic Kingdom, but there is one at the TTC. There are 3 inside Epcot and 1 outside of AK that I can think of.
Can't remember if there are any at DHS. The Writer's Spot at DHS will give you a hot coffee and a separate cup of ice....they even gave me some additional ice so I could get just the right coffee to ice ratio.
What I won't do for my caffeine.....