For rest & recreation, I'd choose either the Grand Hyatt or the Millenium Hilton. Both are on the slopes of Mt.Namsan with great views over the city and the leafy mountain parkscape.
It also makes a big difference in as being able to go for a walk or run in peaceful natural surroundings. Anybody who knows Seoul is aware of how special this really is.
If in Seoul for shopping, both the Lotte (which has a definite luxury touch) and the Westin Chosun have convenient locations close to Myeong-Dong.
For business visits, the Park Hyatt and the two Inter-Continentals in Gangnam are well set in the heart of corporate Korea.
As for "ryokan", the Korean counterpart, Ondol rooms, are available at several hotels. Just ask at time of booking.