I have the deuter (3?) and can honestly say the pram got used less than 5% of the time the backpack did (town and bush) over 2 kids.
So much more practical around markets, city streets, stairs etc, let alone the bush. We take it on holidays - never the pram. Like Rico, i found the kiddies fall asleep in there no problem - disconcerting in the bush when you are ducking trees and hopping rocks and this rag-doll flops all about (but doesn't wake up). Yes, they get heavier when the fall asleep!
With all the gear it does make a fairly heavy load (good for fitness

). I remember once when my boy was nearly 3 - he made it part way up a hill climb and then chose the pack option for the rest. But he proceeded to copy and mock my heavy panting as I carried him the last few km. But give me 10 mins of carrying them in the carrier over 1 hr of carrying them on the hip or shoulders.
The Deuter was pretty good for the purpose, a couple of issue i didn't like. I personally find Osprey packs super comfortable and would have purchased that had they had the model when I was buying.