I'm visiting Seoul at end September / Start of October for 5 nights, and this will be my first time in Seoul / Korea.
I could do with some recommendations for areas to stay. I've been looking at Hongdae, Myeongdon and Gangnam.
It's hard to give recommendations based on so little information. However, in Hongdae, RYSE is an excellent hotel. In Myeongdong, the Le Meridien is the best. And in Gangnam, if you're looking for refined elegance with great fit-and-finish, then it's gotta be the JW Marriott Gangnam.
There is no obvious ranking among those three, unless you give us a bit more detail. But the college crowd will be in Hongdae, and the JW Gangnam is connected to a huge mall. Both the JW and the LM have pools. But in contrast to the JW Gangnam, which does not make for easy metro travel, the LM is very close to metro stations.
For those keeping score, those three I mentioned above are all Bonvoy hotels. :-)
In case you are looking for other picks, I think in Hongdae the Holiday Inn Express and the L7 Hongdae are decent. In Myeongdong, the Aloft is a bit more budget.