Triple Captain is spot on with his info.
The advantages of a Chieftain,
-wing lockers,
-most have the cargo door as standard,
-most have a crew door as standard,
- if you are carrying bulky freight that extra fuselage length could come in handy,
The disadvantages of a Chieftain,
- most have been flogged on RPT so have high total time,
- some were restricted to approach flap setting for landing due to an AD
- AD on the prop hubs aswell in the 90's
- two different engines due to counter-rotating props
- lots of variation in radios, instrumentation etc
- airframe damage around the passenger door from years of abuse etc
- for some they have different brake combinations, which could give you grief in the hip popcket.
Advantages of the PA-31/30
- good performance out of a short strip compared to Chieftain
- only one engine type for the PA-31/310
- still some very low time ones about
Disadvantages of the PA-31/310
- most bulit without crew and cargo doors and wing lockers as these were factory options or not available.
- production life from 1967 until 1984.
Having flown Chieftains on RPT, they are a pretty honest aircraft, just need to be aware of little things such as micro switches on the gear legs, keeping the roller's lubricated on the gear legs, engines normally go full life if you operate them the right way and good endorsement from somebody that knows what the aeroplane.
The nicest PA-31/310 I flew was one with crew and cargo door, wing lockers , 40 degree flap and from memory dual caliper brakes, very sweet to fly and good in an out of short strips. Also flew one of the very first PA-31/310's in the country and that old girl would TAS out at nearly 200 kts at 10,000 feet at 31"/2200rpm. Mind you an old timer had flown in the WA in the great boom of the 60's and reckons the hours on the M/R were fictious when we operated in the mid 90's.