We went for the little life voyager SE for a number of reasons -
It has an adjustable back so can be comfortable for both me and my half pint wife
It has a large storage area so we can get everything we need for a day out in one pack (yes it means that the pack is heavy but it's less hassle than having a pack, and a bag). Our three year old still fits comfortably in it, and because the pack is based around a good rucksack design she's still comfortable to carry.
It has a detachable day pack so that if we're having a big day out, picnic etc we can split the load. This was particularly useful on holiday when we had picnic lunches most days.
The other thing about the little life ones is that they have the pad for the kids head when they fall asleep, a little thing I know but our littlun regularly fell asleep in it, and drooled on it. Being able to take it off and wash it is a big plus!