Depends a lot on what type of forms, if any, you are going to use. If you are using stick on forms both work. Push-ups push the breasts inwards and upwards to create more cleavage. Padded ones give the advantage if you want full coverage that they also have the shape already there! If you are using loose forms or just socks or something go for padded. Sports bras work well with all types of form or sock.
And if you dare get a professional fitting: bra sizes and fitting is a nightmare and you will waste a lot of money on badly fitting bras otherwise. Size varies between brands and manufacturers widely!
Having said that, a well fitting bra is heavenly, especially with good quality forms that will bounce and jiggle like the real thing.