I have a lot to say about this topic.
Baby Jogger City Elite Double Stroller
Pros: Excellent stroller! Lots of pockets in the parent console, easy to open/close, folds flat, spacious, well constructed, sun shade provides lots of coverage with two nice sized windows, vented sides so that it doesn't get too hot for the little ones, reclines to almost flat, seats adjust independently, basket is a decent size, smooth ride, excellent on most terrain
Cons: Heavy, doesn't easily fit in all aisles and door ways (most but not all), brakes and wheels are one piece so if you have a problem with the brakes i.e. strip the brakes, you will have to replace the whole wheel assembly
Baby Jogger City Elite Single with Jump Seat
Pros: Same as City Elite Double
Cons: The jump seat is no longer in production but you can buy it second hand. Note: there was a recall on the seat (the fix requires straps for the sides of the seat). Do not get this seat to use with an older child. There is not enough clearance for the rear passenger's feet unless they are quite small. Finally, it did not feel safe having two kids in the single with jump seat.
Peg Perego Duette
Pros: ability to arrange seats in forward or rear facing, big basket, reclines to almost flat, fits into doorways and aisles, difficult to maneuver on certain terrains
Cons: I did not like this stroller at all! The chassis was not strong enough and wobbled a lot. The seats are hard with no padding. sun shades are too low - definitely not made for taller kids.
If I had to buy a double stroller today, I would definitely look at the Baby Jogger City Select strollers. They are nice looking strollers and I know that they are well made. Good resale too!
I sold it for a fraction of what it was worth and got the city mini - it fits standard doorways and it so light to push, and easy to fold. It was a (corrected age) of about 18 months for us too, we still use it now
