I have been using Avent Manual Pump and now using Medela Harmony in office. Both pumps are functioning well but Avent has many parts to assembly while Medela has fewer and the size (the pump as a whole) is smaller. Hence I would suggest you to buy Medela Harmony. :-P
I am using Avent Manual and Ameda Electric..
Both are good...
Avent: many parts to be cleaned and steamed, and also "air air" sound when pressing it sometimes..... so far, it's quite good