At Epcot, my absolute top choice would be Sunshine Seasons. And that is the best quick service dining in all of WDW... not just for breakfast. I've only gotten breakfast here once but they had a good selection of sugary goodness as well as regular, warm breakfast fare. I think it's convenient to haul butt to Soarin' right in the morning and then hop over to Sunshine Seasons to grab a bite to eat.
World Showcase also has quite a few pastry options. Remember though, that this works best if you start your day later or don't mind eating "breakfast" after you're already in Epcot. 11:00 a.m. is when World Showcase technically opens. Some quick service restaurants will not be open for dining until 12:00 but if I do remember correctly, the "bakery" type places are open right away so you can grab a pastry and some coffee while you enjoy your stroll through the countries. My top choice would be Boulangerie Patisserie in France. It has great setting and if you get there right when they are open for business, you can sit outside when it's nice and quiet.
If you're out for coffee in WDW... well... good luck. haha! Unless you don't mind really bland, watered down coffee... i'd steer clear. That is, of course, unless you know where to find the good stuff. In Epcot, Fountainview Cafe has some latte and cappuccino choices that will mask the nastiness of regular WDW coffee. The Writer's Shop and Starring Rolls at the Studios also have more than just plain coffee. But the absolute cream of the crop is Kona Cafe in the Polynesian Resort. You can get AMAZING kona coffee at the Poly. Just another reason why Poly guests are so darn lucky.
The only place in the Magic Kingdom that I would suggest would be the Main Street Bake Shop. I have to stop here every vacation to grab a cheese danish. MmMmMm. The line will probably be long and you probably will get hit in the ankle with a stroller but it is all worth it when you get that sweet goodness. :)
Animal Kingdom's breakfast choices are actually quite large if you want a sit-down restaurant. The one quick service place that sticks out in my mind as being pretty awesome for breakfast is Harambe Fruit Market. You can get lots of fresh fruit here which I think is pretty cool. As far as the Studios goes, i'd say that your best bet is Starring Rolls. I just think that the Studios lacks in quick service dining options and I wouldn't waste your time looking for scrambled eggs that actually taste good. When it comes to quick service in all of WDW... stick with the basics.
I'm a big fan of WDW table service breakfast! I normally do one restaurant per trip. A lot of people really love Crystal Palace at the Magic Kingdom. Well, i'm going to have to disagree. I've done dinner here twice and breakfast once. The service was slow every single time and it was just so darn loud all the time. Two characters actually avoided our section on our last visit to Crystal Palace and we were there for over an hour and a half! In replace of CP, i'd advise going to the Polynesian Resort which is just a monorail ride away from MK. Hit up Kona Cafe!!! Get a pot of kona coffee and some Tonga Toast. This is my favorite breakfast on property. The service is great and you get to be at the amazing Polynesian Resort! Get the earliest reservation you can, eat your meal, and then take the monorail to MK.
If you have any questions on breakfast at WDW just drop me a line and i'll be happy to help!