Scuba Diving in Croatia (Vis, Hvar, Split or Dubrovnik?)

I have an extra day in each of these cities and i'm looking to get in one or two dives.

I was hoping to go to the blue grotto from Vis, but I'll be there early July so i feel like it would be pretty crazy. Has anybody been during the busy season? I was wondering if it's really not too bad or something that should be avoided.

If it is, is there anywhere else in Croatia that has really good scuba diving? I don't really care much for wrecks and am more interested in seeing colourful corals and marine life (to get a wreck with lots of fish would be a bonus, but as far as I can tell, you generally get one or the other).

Also if anybody has the name of a diveshop they'd recommend then feel free to chime in here,

thanks for the help