Take the bus from the airport to the hotel. You'll be delivered to the hotel front door. By the time you are ready to return back to the airport, you'll be more familiar with how to get to the MTR (metro) station from the hotel, and you can choose whichever seems best for you.

When I went last year (first time in Korea), I researched the options and decided to take the bus from the airport. On the way back, the convenience of the bus outweighed the extra cost for me, so I took the bus back too.