Depends what you want it for - if you want to soley express then I'd definitely go for electric or you'll spend your life pumping!
If it's only occasionally so you can have a break or OH can feed, and you haven't got £80+ to spend, then manual will probably be all you need. Obviously if you can afford electric then it's best - quicker etc, but all comes down to how much you wanna pay. HTH x
ETA: I bought a manual one as I only plan to use it occasionally, plus I didn't want to fork out lots of money when I don't know if I'll be able to express/breastfeed. I'll see how I get on with manual before deciding if I want or need electric x