Far and away, Mandarin oranges. But you’ll have to go to China to get the real thing, most particularly Western China in the Yunnan and Sichuan provinces. They are the best tasting, most easily peeled oranges in the world!
I know that tangerines are too tiny for your parameters, but Honey Tangerines are some of the best citrus fruit I’ve eaten! They’re juicy and a little sweet and better than any other oranges I’ve tried from the food store. Of course if you can, order Red Navel oranges during the winter directly from Florida…they’re the best if you want huge, ripe oranges.
I agree with kay. When I was a kid, I worked here packing citurs for gifts, and we got to eat all we wanted. The Honeybell Tangelos were the best! The season for them is over now tho, so I don’t think you will be able to find them. At least not from that area of Florida.
Navels are the way to go if you are looking for both size and peel-ability, but if you are looking for flavor and something beyond easy to peel with moderate size Temple Oranges are the way to go. The best I’ve had of both came from http://www.orangesonline.com/oranges/, they supposedly get the top 1% of the crop.