Fiqh-us-Sunnah Volume 5, Hajj and ‘Umrah, Fiqh 5.110.

There is consensus among scholars that a sacrifice must be of one of the animals, and that the best of these are, camels, then cows, then sheep and so on, for a camel is more beneficial for the poor because of its great size (more can benefit from its meat), and similarly a cow is more useful than a sheep.

There is disagreement, however, as to what is best for an individual to offer in sacrifice, a camel or a cow sharing one seventh of their price, or a sheep. Apparently the preference in this regard is to what is more useful and beneficial for the poor and the needy.