What cattle do we get our "beef" from in the US?
As someone who has raised beef cattle (here in Oklahoma) I must say the TFD is (unfortunately) mistaken, (at least here in the U.S.) Most cattle fall into one of two varieties, Beef and Dairy (there are also some breeds that are almost exclusively show cattle) The most popular (and common) Beef varieties are Angus, Limousine, Herefords, Longhorn; This list, including cross breeds (for instance, limangus, what I raise, is a cross of limousine and angus) and constitutes somewhere around 90% of beef production with in the US. (not include 'beef' used for things like dog food). I would consider that list to be in descending order of beef quality (but that is a matter of opinion...)

There are several varieties of cattle which are raised for dairy production, and these do not generally produce quality cuts of meat, but do produce copious quantities of milk. These breeds are led by Holstein-Friesian, Brown Swiss, Guernsey, Ayrshire, Jersey, and Milking Shorthorn. 

Buffalo (or Bison) is a separate breed altogether and is no longer all that exotic. I regularly use bison to make chili. 

Yes, cows are 'females' but not all cows are heifers, a heifer is a female that has not yet given birth to her first calf .

And @Scivitri while feeding and ranging cattle do make a difference the driving force in beef flavor is still the breed. I can tell the difference between breeds by flavor but the difference from feeding and ranging is really more about tenderness and texture.