Either option can be a good choice; it depends more on how you shoot than on image quality or speed, since the cards are otherwise similar.

Two 16GB cards give you some redundancy in practice: if one card fails or is damaged, you only lose the images on that card, not everything from the day. They also suit slower-paced shooting where swapping cards is easy.

One 32GB card is more convenient for long sessions or fast-paced events because you won’t need to stop and change cards as often. That can reduce the chance of missing moments or misplacing a card during a swap.

In real use, card-handling mistakes can be as big a risk as card failure. Whatever you choose, avoid removing a card while the camera is writing, power the camera down before swapping cards, and properly eject the card from a computer before removal.

So: choose two 16GB cards if you value splitting your risk across cards; choose one 32GB card if you value convenience and fewer card changes.