mamamila The main reason I chose the vibe is because I liked the idea of being able to fold it with the doubles seat still attatched, we've got six children so space in the car is limited and I don't like having different parts of the pushchair all over the car.
Other considerations for me were:
I prefer the strap recline mechanism on the vibe to the zip reclines on the sport
The proper sun-hood which gives great coverage and can be positioned anywhere on the frame as it slides up/down freely
The handlebar break on the vibe is so much easier for me than the foot brake on the sport, I found it really hard to do on the sport.
I don't know much about the Dash other than the recall regarding the handlebar problem so that put me off buying s/hand dash's.
HTH