For the children, I have to say we have the city double, and they love it! Things we love:
-Two seats are separate, so can recline independently
-Canopies adjust independently, and are detached from rear, so can swing all the way forward
-The handlebar adjusts to infinite # of positions, from vertically up to vertically down, great for tall husbands and ambitious 2 year olds.
-Very easy to push and steer, literally one-handed when I'm carrying the baby!
Things we don't love:
-no snack tray for the kids
-heavy as all get out, its half my workout just loading/unloading
-the forward fold is awkward, doesn't lock in folded position, and therefore difficult to move around folded (and lord help you if you need to store this folded in a closet as I thought I was going to do! Now it stays in the back of the truck.)
- no tether for jogging safetly, though I suppose you could improvise.
And if you haven't guessed, we've used it only sparingly for running. I was a runner once upon a time, but now walk mostly.