i haven't used BJT's for ages, i would go with discrete mosfets as there is virtually no static gate drive current requirement (dynamic is another issue) and modern mosfets have near zero conduction losses, darlingtons have around 1V Vsat or worse which is why you need a heat sink not to mention losing that valuable volt across the load,
a few Amps w/ RDSon in the tens of milliOhms hardly requires a heat sink at all, just a flea spec on your board might do it

additionally you often do not need the base resistors for gate drive

what exactly is your load and switching speed ? and number of channels ? and operating voltage for what is presumably a PIC driving these ?