Girls, what do you think about the push-up bra? And Bra-less-ness?

I love when I dress-up to feel feminine and sexy. depending on the outfit, sometimes I don't wear any bra or sometimes I wear a push-up bra. In each case, my breasts ache, sometimes for a couple of days and I am wondering what are other girls' experiences?

It's similar to the ache from wearing a ponytail for too long, but in the breast.

What brand of push-up do you like and do you think it's not bad to wear them? Does it hurt anyone else to go without a bra?