Loved my Medela PIS. Used it for both kids, 15 months each (I returned to work at 8 and 9 weeks, so for the first few months was pumping 2 - 3 times a day). It's in great shape - I sold it to my neighbor (she bought all her own tubes and bottles) and she used it for about 12 months, and is going to use it again over the winter. So you definitely get your money's worth!
The second time around I had the battery pack which was GREAT - the first time I had used the car adapter which was fine, but the battery pack definitely made it more portable.
I also had the Avent Isis hand pump and I must say for a hand pump, it was great. It was nice to have for those times when I didn't want to lug the whole pump around, or (the first time, before the battery pack) I couldn't get to an electrical source (theme park, airport, etc.)
I don't know anyone who had the other, so I can't comment on it. EVERYONE I know has the PIS. I bought mine from an internet store and got a pretty good deal, just do your research first and make sure it's an authorized distributor so you know you're getting a new one.
I love the secret club we have where I work (a building with about 3000 people in it). We have lactation rooms and whenever I see a woman walking to or from that area with the PIS shoulder bag or backpack, we kind of give each other a little sly grin... like "I know what you're doing, none of these guys has any idea, though!!"
Good luck with your decision!