I’m trying to decide where to go from Trogir while heading south to Dubrovnik in early May. I’d like to drive to either Korcula or Mostar and spend one night before arriving in Dubrovnik for 3 nights. Once in Dubrovnik, we will take day trips as well. Thanks to all for your input.
Early May means the season hasn't really got going on the islands. Personally, I wouldn't bother with the hassle of taking a car onto Korcula just for one night plus much of the accommodation has a 3 night minimum booking. Mostar or Makarska on the mainland would be good alternatives to Korcula.
Three nights means two days in Dubrovnik, so you haven't got much time for day trips, assuming you want to spend some time in Dubrovnik itself.
I assume you know that driving to Korcula means taking your car on a ferry. Also, in early May ferry schedules will limited; the full summer schedule doesn't really kick in until June.
For those reasons, I think you're better off doing Mostar.
Both Mostar and Korcula are worthy destinations, but for different reasons, and I wouldn't say one is better than the other on their individual merits. Just that I think logistically Mostar is a better option for you.
Make sure your rental car agreement allows you to drive into Bosnia/Herzegovina.
Thank you for your advice. Mostar and Medjagorie it is.