There is really nothing much to say except there are 2 kinds:
1. Cylindrical-shaped bristle/sponge head, with twisted wire handle
2. Like a gigantic toothbrush, slightly bent.
My personal preference is actually the second type.
But whichever kind you get, do remember to also get a teat brush, which is like a small, cone-shaped bristle head, to reach into the teat. (The smaller brush in the first picture.) The brand PiyoPiyo even carries a straw brush which is so tiny it can clean the tiny hole of the teat.