Without knowing all the details, this appears on the surface to be a no-brainer. Take the Caravan job! Great airplane, and FedEx feeders use the type...may open a door later on you didn't know was there.

Also, I got hired flying regional jet with more piston twin time than normal, and lost a recent job prospect flying King Air 200's because I specifically had no turbo-prop time. Ouch! If I'm not mistaken, the Caravan uses the Pratt PT-6 also, and will give you knowledge of turbine engine management.

Just something to think about.