In reply to dsh: Sounds like we did the holiday you are planning last summer as a family holiday (2 climbers out of 4)so needed a balance of activity's
Will agree with most of what has been already posted, especially that it is very hot in the summer!!
We spent 4 days in Split which we thought was brilliant, stayed in a city centre apartemnt and climbed at Sustipan (DWS) and Marjan. You can hire bikes and cycle to Marjan right along the sea front (lots of beach bars on way back to rehydrate)
We then headed to Hvar,which is even better than Split, easy ferry from centre of Split to Hvar Town (by far the best place to stay). We had an apartement in the Podstine area of Hvar town,which by luck was 5 mins from the crag at Podstine which was excellent for evening climbing.To get to Cliff Base (best crag) you really need a car which can be hired easily and cheaply from Hvar
During the day you can hire small boats and climb on the seacliff end of Podstine crag, lots of unclimbed rock, my son put up several new DWS routes on a crag only accessable by boat. Lots of excellent bars on the islands opposite Hvar to visit. If you want some accomadation, snorkelling and crag info pm me
Rob