what are the needs here? what busses are available, ESATA, USB 3.0, SATA?
internal will generally be fastest, followed by ESATA (unsure about ESATA and powering down), USB 3.0 would be next.
I would suggest a large TB+ size drive on the sata port mounted inside the computer.
USB 3.0 ports will ususally be blue. if they are black then the bus is too slow for storage uses.
WD drives 101 Made easy by color codes
RED drives are for Network Attached Storage.
BLACK fast performance drive with a long warranty. I suggest these for you
GREEN low power low speed drives mainly for external use
PUPRLE are for Camera Storage systems and are tailored to that workload
BLUE desktop class drives with a good rotation speed
All drive makers have different drives for different workloads but WD is nice enough to color code it to make it easy