This is personal preference. Going to be using your breast pump a lot? Then an electric one may work best for you. They’re fast and can help to save your wrists and hands from aches and pains that can be caused by prolonged manual pumping.
Only going to be expressing occasionally? Then a manual, hand-held pump may be the best choice for you. They can be quieter, easier to use on the go, and mean that you're totally in control of the pace at which you pump. This can be appealing to some parents who may find electric pumps a little daunting when they're just getting started.