Regarding Swiftair...
They are partly a Pay-to-Fly Airline where young, inexperienced pilots PAY the Airline over 30.000 euro just for the right to work for them a couple of months. After that, they are often kicked out and replaced by new ones.
This is certainly the case on ATR42/72. I don't know if they do this on MD83 and B737.
The crews I have met however were all nice, professional but critical of the practices and work ethics of their Upper Management.
I do know that the technical status of their B737 fleet is often questionable, resulting in them seeing their DHL work reduced very recently due to reliability issues.
I do doubt though that Swiftair crews would go airborne with an not airworthy aircraft.
Swiftair also has good Africa experience, flying B737, MD83 and ATR's all over the Continent.