Is South Korea a better holiday destination than Japan?

Or is it the other way? What's in Korea and what's in Japan?

I've been to both Tokyo and Seoul and in my opinion, the two countries are very similar. They're both crowded, congested, and filthy expensive (only in certain areas though). Personal space is non existence and everyone is in a rush. Although, people were extremely polite and both places are very safe and clean. Although, Tokyo tended to be a bit cleaner than Seoul.

However, my advice to you is to buy a ticket to San Francisco bay area and enjoy the golden gate bridge and visit Chinatown, Japantown, and the unofficial Koreatown in Santa Clara. Same food, same group of people, and you can tour Googleplex, Yahoo buildings, eBay, youtube, Stanford, ... all in one day. High Tech, natural beauty of the bay, GG bridge, Coit tower, ... Save yourself the headaches of international travel and go to San Francisco. And you're only a Bart ride away from Berkeley as well.

both will be nice

korea is a little cheaper than japan but seoul can be expensive if you are british it will be very cheap for you and not as many people go there so you can just have fun get lost and explore the streets of seoul which is one of the biggest cities in the world not to mention korean food is great not as good as chinese but better than japenese

Buying had some good points. I have lived in both teh Tokyo and Seoul areas for several years. If I was going to vacation, I would probably go to Japan during Cherry Blossom season. (avoid Korea during same springtime due to Yellow Dust season) I would also choose a secondary city, like Kamakura, Kyoto, etc to pair with Tokyo.
A lot of the beauty in Korea lies south of Seoul. You would need a car and some knowledge of the areas. There are trains but many temples and hikes are diffficult to get to from teh bus stops. Also, jeju island would be a great stop but require a boat from Busan or short plane ride.
Japan is easier to traverse by train.. trains stop in center of tourist areas or all is reachable by trains.. not so in Korea. (outside of Seoul)
even the attractions near Seoul like Korean Folk Village or Everland are much easier with a car... no direct train. (buses are not as easy here)

If you want to have a great time without having to spend a lot of money I would choose Korea over japan.

It entirely DEPENDS on what you want to see and do.

No doubt that both countries have sights and things that appeal to everyone. What appeals to you?

Btw, Seoul actually ranks higher then Tokyo in terms of expense.

1. Moscow
2. London
3. Seoul
4. Tokyo
5. Hong Kong

I suggest the original poster research on wiki travel and check out some guide books for both counties to see which they would like to visit. Flights between Tokyo and Seoul are not terribly expensive so maybe the poster could travel to both countries on a larger trip.