Dishwashers are not common in Korea (my wife thinks it's partially because the sticky rice hardens on the plates rather than getting removed, so those who try don't have a good experience with it).

I'm so happy to have one.

But if i have to vote, i'd probably choose the coffee machine. It's advanced enough to take in whole beans and serve us with fresh coffee every morning. My wife used to spend fortunes on Starbucks; she barely goes there now that we have this machine.