Things to consider :-
1) Number of seats - You have already decided.
2) Field types and length - Are any short or rough strips expected
3) Sector length - STOL capable types tend to be a tad slow for anything over about 250 miles
4) Support - generally better for big names like Cessna or Beech, what do the local FBOs and workshops support.
5) Turboprop or jet - Small jets use more fuel, have very cramped cabins and poor short field performance - only consider for longer sectors.
6) Crew availability - Plenty of Caravan or KingAir pilots around.
7) Load capacity - If you are taking tourists to & from hotels they will have a lot of heavy baggage to consider so you may need a larger aircraft.
8) Competitive pressures - If seat price is an issue you need to keep costs down with something like the Caravan.