I actually prefer sealed burners. However, you can still get whichever you want.
Unsealed (or open) burners are more exposed to oxygen and burn more easily. They give direct heat to what's above them, and you can control the flame better too.
However, you'll need to clean open burners more often.
On the other hand, sealed burners are easier to clean while also performing more or less as well as unsealed burners.