I would recommend that you read the reviews at
http://loungereview.com/lounges/airport/ICN/ in order to form an opinion.
A key point to keep in mind is that you cannot get to Concourse A unless your flight actually departs from there (or, to be more specific, you can, but then you won't be able to come back to the main terminal and will have to request an escort - don't do it.) So this may effectively reduce your options.
The most generous buffet is at the SkyHub lounges, followed by the Matina lounges. The latter are technically the executive lounge within the airport's transit hotels.
Food aside, the Asiana club in the main terminal is the most beautiful lounge. The Asiana lounge in Concourse A does not have windows. The KAL club in Concourse A is... interesting. The design can be an acquired taste.
I'd grab food at one of the SkyHub lounges prior to heading to the Asian club in the main terminal.