As I said, it really depends. For a mission that would be more than 50% time in a hostile space, I'd definitely took something more maneuverable. So... well perhaps the Serenity. Decent cargo, good armament, small for it's cargo and good turnrate for transport. Doesn't get stuck in lanes at all.
But if the hostile space would make under 20% of the route, than I'd say grab some transport, park liner along the way and go. Or take Serenity anyways