Whether you'll choose manual or electric, a single or double pump will depend on how you plan to use it.
Time is the single biggest factor in deciding.
If you know you'll be pumping at work and want to make that time as short as possible, you'll need an electric pump that is reliable, quiet, and fast. If you'll only pump once or twice a week, a manual pump will serve you well. If you plan to return to work right away, buy the best pump available. Even if you don't plan on returning to work immediately, a breast pump can make the process of breastfeeding simpler and less painful - but you can go with an electric or manual pump meant to be used two or three times a week and save a lot of money.