Ok, here's my pros and cons of the two Major Contenders for best double electric pump. The two I'll review were the two I used for my daughters: Avent ISIS iQ Duo Double Electric Breast Pump for my first (shortly after it came out) and was pumping for 9 months, every workday, 2-4 times a day. For my second, I went with the Medela Freestyle, and was pumping every workday, 1-2 times, for 6 months.
Features common to both: Both pumps are adjustable in strength and frequency of pumping action, and both can be customized with soft breastshields (these come standard with the Avent IQ). Both are now BPA-free (though when I used the Avent IQ Duo, it was not, but Medela has always been BPA-free). Both can also be used as a single pump if you want to, for example, pump one side while your baby feeds on the other (I never managed this, since daughter would get distracted, but it seems like an efficient use of time). Both come with a carry bag, basic bottles, cold bags and cool packs. Both are compact, and look reasonably presentable (the Avent more so), if you forget to tuck it into a desk drawer before a meeting.
Features specific to the Medela Freestyle:
Hands-free use: The freestyle earned its name because it can be clipped onto your belt, and the horns used hands-free. Unlike previous Medela pumps which required further attachments and Medela-brand bras, these can be used with most brands and styles of nursing bras. HOWEVER, I found the hands-free system to be uncomfortable. It is possible that this was a feature of being relatively well-endowed (around 36E/F, while breastfeeding), but in the end, it didn't prove useful for me. However, I still appreciated the compactness and cord-free operation, especially while my pumping situation at work was influx.
Cord-free/rechargeable: In keeping with the hands-free, it wouldn't be much help if you needed to plug in. So the Freestyle can be charged and then used for a while before needing to be charged again. I don't remember how frequently I charged it, but it was probably after several hours worth of pumping.
Travel-ready: In addition, it works in 110-220V sockets, and comes with a variety of travel adaptors.
Adjustable strength/speed: The Freestyle has adjustments you can make: to the strength and speed of pumping action. These are controlled by up and down buttons on the main device, and have a range of about 5 settings. There is also a "letdown" button which you can push after your milk starts flowing, and it will speed things up and intensify them by about 1 notch on each.
Features specific to the Avent Isis IQ Duo:
Intuitive strength-speed controls: The major winner for the Avent IQ Duo is its intuitive control system. It works a bit like cruise control in your car! The controls are in the powered pump horn, rather than on the main pump unit. The powered horn looks a bit like a regular, manual pump, and you can use it like one, except that it will control both horns. But, you pump at the frequency and intensity you like by squeezing the lever as frequently or far as you want. This is especially helpful for stimulating letdown. Once letdown is achieved, adjust your pumping rate/intensity to whatever feels right that day, then press the blue button and the pump will continued at this setting until you change it again. To change it, what do you do? Just start squeezing the handle again to regain "manual control" and set the blue button again afterwards. It doesn't get easier than this.
Better storage bags: Ok, this is definitely tangential to the main point of choosing a good breast pump, but the bottle storage bags that came with the Avent Duo were just easier to use than the Medela's. They're two tubular, thinsulate lined bags which fit one bottle each (two if you squeeze) and soft gel packs. The size of the bags just fit inside my laptop bag or backpack better than the large Medela cube. (On the other hand, Medela's travel bag was better than Avent's--smaller, and easy to fold up if I pack the Medela into something else.)
Soft breastshields come standard: The Avent comes with soft breastshields as included. They also have these little bumps in them that are supposed to help stimulate letdown. I'm not sure if they did, but I do prefer the soft breastshields to the hard ones.
What's the bottom line? Well, for my second daughter, the Medela Freestyle was right since we were moving from the US to the UK, and doing a lot of travelling. On the other hand, with my first daughter, I pumped longer and found it a less onerous task in general. This was for a number of reasons, but I wonder if the ease of pumping with the: Avent ISIS iQ Duo contributed.
