Hvar or Korcula?

Korcula.

Going with your criteria-I also say Korcula.

We loved Korcula - was one of our favorite spots in the area. A day is enough (we stayed two nights and one full day, which was perfect). Hvar struck us as kind of tragically hip and pretentious, trendy and a bit full of itself. We were only there for half a day and that was plenty. If you want to disco till dawn with the beautiful people or drink till dawn with the backpacker set, my impression was that Hvar would be the place. If you want something more quiet, with less crass commercialization, pick Korcula. Note that the time of year you go may have a big influence on how any of these towns seem to you. They all get busy in high season. Shoulder season, some are still busy but others seem to drop off the tourist circuit. BTW, if you love walled cities, old towns, etc., see if you can squeeze in a short stop in Sibenik - a brief (few hours) stop is worthwhile. It's not mentioned in Rick's book but we were pleasantly surprised. Lots of steps, though, so if you go, be ready for some burning thighs.

I will have to admit that I am a bit bias as I live on the island of Korcula 6 months of the year, so I would pick Korcula over Hvar. It has a walled city with lots of little walkways to climb up and down. The view is incredible. Lots of little cafes to take in the sites and people. You mention a "day"in Korcula or Hvar. Becareful because sometimes you cannot come and go as you please. What I mean is this: if you are coming from Split for example then there is only one boat everyday, leaving Split at 4-5pm depending on the time of year. Which means you would have to stay overnight in either Hvar or Korcula. THEN there is only one boat that leave from Korcula or Hvar back to Split and that leaves at 6am...so infact you will have to spend two nights in order to have one day in either town. Whatever you do, you will love it! Enjoy,
Lynda