Brass or Steel ?

In my previous post I show 2 new gadget for the bunnies, today I'll post the same item, the nipple head, but from different material.

On my last post the nipple head was made using brass, but this one is made of stainless steel. After a few consultation I got from fellow breeders, they said that the brass can rust over a few period of time but not with the stainless steel. So, they suggest that for longer performance, the stainless steel is the best.