At the Farmers' Market: Tangelos
Tangelos, then, are a tangerine-pomelo (think grapefruit, but with a much thicker rind and green on the outside) cross. Down in Georgia, the first place I ever had one, they're called "honeybells" due to the nub on the stem end of the fruit.
The reason to buy a tangelo is ease of eating out of hand. The flavor is that same sweet-tart that's found in Cara Caras (but a little sweeter); the nice part is that underneath the nub is good old-fashioned air, so you can seize a fruit by the nub and bend it back to peel the fruit. Eat it as is, but for a breakfast treat, squeeze the fruit to express the (usually copious) juice.
As with any citrus, buy fruit that is unblemished (small brownish-grey "seams" are not a blemish, just a mark from where the fruit touched a branch) and relatively heavy for its size. The more bulbous the bottom, the more juice the fruit will contain.