Each to its own, you are dealing with airframes that are between 30 and 22 years old.
The Mojave has the added advantage of not having geared engines and also having a cargo door to load a stretcher through, the disadvantage is that only 50 airframes were built and Piper has changed hands so many times in the last twenty years spares could be difficult.
The C421 has the advantage of more airframes with some being built as late as 1985, but on the downside the GTSIO can be joy to operate or a maintenance nightmare.
Nothing cheap about operating a pressurised twin!
Just ask the f#@kwits that operated a Mojave on a bank run.
Is it private operations or charter