Fi, I've only ever had a manual Avent one, but I did express for 2-3days per week for a loooong time.
I found the Avent one to be great, I'm not sure what your definition of slow is though. It used to take me about 30minutes to get 200ml out of both sides (15mins each). Towards the end that slowed right down though to about 100mls sadly.
Unfortunately no matter how much milk you have a baby sucking is always going to be more effective so sometimes you have to pump more often than she would feed. Like when I did night work I would pump a couple of times even though DD only had one feed overnight.