they both work fine. i currently use a 16gb, and my friend just got a 32gb and says it works fine.
the 32gb is currently, afaik, sold exclusively on the sandisk web site for $199.99 USD.
the 16gb is on the sandisk site for $108.99 USD, but i've seen them for as low as $31.43 USD elsewhere on the internet. i got mine on sale for $59.99 USD at bestbuy a while back in '09.