Unfortunately, it's been exactly two years since I've been to Seoul (one of my absolutely favorite places) - so I cannot offer any COVID-era experience.

That being said, I'm partial to the Park Hyatt provided you are fine with it's COEX location in Gangnam (a bit away from all the touristy/cultural locations in Seoul - but everything is easily accessible via Metro). I just really love the Park Hyatt's style and how they've incorporated many traditional Korean elements into the design - I also think they have some of the best service of any hotel I've visited in Seoul over the years. The Grand Hyatt is in a better location for tourism and business work in downtown Seoul. Service there is good and they have a club lounge (although I believe it's currently operating under modified hours).

I've yet to stay at the Andaz Seoul, but based on what I've read when it opened I probably would have just picked the Park Hyatt again if I needed to bein Gangnam.

Pretty sure all properties (except Hotel28) have a dedicated thread here on FlyerTalk that you can reference for more details.

-FlyerBeek