After coming back from 2 weeks charter in Croatia I can recommend Ban-Tours Yachting: Ban-Tours yachting
I have booked very early with them on the Dusseldorf boat show for a good price. They are the Dufour dealers on Croatia and have a small fleet (13 or 14 boats). They are all very recent boats (mine was 5 months old). They have only Dufours from the performance line and from the cruising line (Grand large).
This is a small charter company and that permits a personalized contact and Ana, the girl that takes care of the paper work and Anton, the owner are not only impeccable, but also very nice people.
Anton is a sailor and a relatively young guy (about 35). Before starting the charter business he was for many years a skipper and you can fell that. I mean that you are talking with a sailor and not with a businessman.
The base port is marina Frappa (Rogoznica) and that is a good place because it permits you to go South, to Dubrovnick, Korkula (and other nice places), come back, stay on the marina again for taking water and some supplies and then head North, to the national park and the Northern Islands. That way in two weeks, we only stayed on one Marina, the Base (free of charge) all the other days we stay anchored or on buoys, in nice places (and that's easy because there is lot's of good and nice places to stay sheltered from the wind).