I'm not a mom of multiples, but I have tried most of the double electric pumps out there and my absolute favorite is the Whittlestone Expresser! The expression cups consist of soft blue foam covered with thin flexible silicone. Between the two is a cushion of air. There are two air tubes for each breast cup. One provides continuous suction (unlike all other pumps which suck and pull the nipple then release it), and the other tube provides air to inflate and deflate the air cushion which massages the areola. The continuous suction not only makes this a more efficient pump, it also eliminates nipple trauma. I learned about this pump from a support group for women trying to induce lactation. Many of them were using this pump in preparation for breastfeeding an adopted child because it most closely mimics a baby nursing. It definitely doesn't hurt and I even found it to tickle a little sometimes
I've also used the Medela Lactina (at the hospital) and the Medela Pump In Style Advance. I think most people use the Pump In Style because Whittlestone is a small company and doesn't have much advertising. If they were as well known as Medela, I'm sure they would lead the market! Medela advertises their 2-phase expression as "the only research-based breastpump technology that mimics a baby's nursing rhythm." Hummm....whatever. Basically it starts off with a minute or two of fast suction and then goes to a slower suction. The goal is to mimic a baby stimulating the nipple to achieve let down and then slowing down once let down has occurred, which according to Medela, happens for most after that 1-2 minute time period. I do like the backpack and the way they have the pump in the bag, but I guess I don't think it's worth $300. (http://www.medela.com
Similar to the PIS is the Ameda/Hollister Purely Yours. It is also a double electric and you can adjust both the suction and the speed, whereas with the PIS you can only adjust suction (if memory serves). All three pumps come in a nice black carrying bag or backpack so they look professional if you have to go back to work. You can get the Purely Yours in a desktop model which doesn't include the bag. The Purely Yours is so light that I would suggest this route. Just buy your own bag and put the pump in it. The others are too heavy and cumbersome for this. The desktop model is also WAY cheaper. All of these pumps are around $300 new, but I was able to get my Whittlestone Expresser for $160 on Ebay and the Purely Yours desktop model for about $120 new. I think I paid full price for the PIS. The Medela Lactina was at the hospital but was pretty much the same in terms of performance as the PIS. The company that makes the Purely Yours also manufactures the PlastiBell circumcision device, so many people don't purchase products from them. (http://www.hollister.com/us/mbc/breastfeeding/products
poorly designed website alert!)
I found the Avent Isis to be completely useless, but others rave about it. Another factor to consider is that Avent also manufactures bottles (formula use) and pacifiers. Some prefer to support only companies which make breastfeeding products.
This was probably way more info than you wanted, but if you have more questions, feel free to ask them here or PM me!