Piper PA-31/310 good all-round performer, still a few low time models around that would fit the bill.
Shrike 500 is a lovely aeroplane to fly but has stuff all passenger appeal and is pretty cramped cabin.
C90 Kingair is a good performer, nice big cabin which gives that big aeroplane feel for the boss or charter clients.
B200 Kingair has to be the star of the class, but has the boss got a good heart for the retail prices of the spares?
B350 Kingair great aerplane but you start to get into the joy of operating something above 12500lbs.
Forget about Senecas, Aztecs, Barons all lots of limitations and not really genuine six seaters.