Valencia oranges. Thin skinned with lots of seeds make them difficult eating oranges but they have superior flavor and are excellent for juicing. I even augment prepared juice by juicing a couple of them into the amount I'm serving.

My father squeezed fresh OJ every morning all his life. He only used juice oranges. They tend to be smallish, with mottled coloring and will not win a beauty contest - they seem very unpromising. But they yield the most juice and the most flavorful juice.

I'm in CA and we always use Valencia oranges. They are the thin skinned variety and they yield more juice than most.

Thin skinned oranges, that feel heavy for their size. Usually labeled 'juice oranges.'

Navels often yield relatively little juice, since they're thick skinned, with lots of pith (which of course, makes them easy to peel and eat out of hand.)

Blood oranges are also good - gorgeous ruby color and great flavor. Very lush looking.

i look for the "juice oranges" at my market. they're have slightly thinner skins and are very, very juicy.

I personally love navel oranges for juice ...