Out of them all, the PA31L would be a suitable private aircraft. Flown by one or two pilots, with good TLC maintenance, it should perform well for many years. Its as easy as a Navajo to operate and operated in the 16 - 20,000 region provides good range. Like all aircraft, even though de-iced, they accumulate ice pretty quickly and performance decreases. Its better to get out of ice as soon as possible.
From memory the C421 was heavier, but carried more fuel and operated nicely around the FL200 mark (especially the C Model), but he engines were a problem (even when shown lots of TLC). Perhaps Gaunty can fill us in on his experiences with the C421?
The PA31P was a man's aeroplane. GTIO - 541 engines - 400 hp on take off, noisy outside, smooth inside. Drank fuel, you could use up the aux's just climbing to FL200. Qld government had one (VH-SGA) and the old Air Tas operated BSF on aeromedical flights, until one clown ran a tank dry and switched tanks without closing the throttle, the resultant surge caused a counterweight to smack the bottom of a piston, which slowly came apart and on the next flight filled the oil filter full of metal, and was shut down due lack of oil pressure. Last I saw of BSF was outside GAM's hangar at Essendon. Although I do remember hearing that the owner used it on a rain making contract after that.