We don't have the expensive ones- Have Graco Duoglider (front to back), Graco side to side and a sit and stand- my kids are 3 1/2 and 1 1/2. The front to back is not good because dd in the back kicks ds in the front too much and it is hard to get her in and out now that she is bigger.
I like the side by side (sit and stand was hard to push)- they can get in and out easily and the weight is more distributed, rather than having to rip my shoulder out of the socket trying to push!
What I really wanted to say was if you have time, look at garage sales for a double- your kids are getting older and you probably don't really need one except for trips like WDW or a zoo or something. I got my side by side and sit and stand for $20 each at a garage sale. Now I hope nothing happens to them, but if it gets damaged on the plane or something, I am not out a ton of money for something I won't use often anyway!
Good luck finding something you like!