I just did all of this research and it's important to know what YOU WANT and go out and look at the various options. Merry Go Round in Bellevue has a few double strollers and can tell you the pros and cons of each. You can also search in Google for sites with opinions.
I love to walk outdoors with my kids so I definitely needed something for that. For trips to the mall, I use our Bugaboo stroller with a toddler board--easy to get in and out of the car. For walking and the zoo, I went with a Baby Jogger double stroller b/c of the following:
1. It's large enough for my 2 year old to fit in now and a year from now. (the Mountain Buggy will not hold a 2 year old b/c it's not high enough or wide enough)
2. It has a walking and running option where the wheels will lock or swivel.
3. It's small enough to fit through doorways.
4. It load balances so it doesn't steer to the side of your heavier child.
5. It has the best sun canopies so my children will be protected from the sun.
6. Each seat reclines so one child can take a nap.
7. It has some sort of patented system to make it easy to close. Regardless of the marketing, it is extremely easy to close.
These types of strollers are heavy to put in the car. This one is 35 lbs so I definitely use it for specific trips. It's not that hard to place in the car now that I'm used to it. Also since my 2 year old likes to walk in stores and the mall so I never planned for her to use a stroller at this stage.
For me, I didn't like the front/back strollers b/c it's not a option that will last for a few years. I hear the youngest child is in back and once they are 1 then they can kick and push on their older sibling. However there are plenty of moms in New York who use this option b/c of the narrow sidewalks that I would search out their opinions of the pros and cons.
Good luck.