We have a Graco mosaic one travel system. We got it because it was light and compact, and would fit in the back of our little car. It's been OK while DS was small, but at 5 months there's no way in world I can lift him in his car seat. I now just use the pushchair bit, but DS is getting heavier, and one of the wheels has gone funny. It's getting really hard to push, and i'm aware that my posture is awful when I'm pushing him because of the amount of effort it takes.
I'd really like a light weight pushchair that folds down small, that has adjustable height handles, that is sturdy enough for me to lean on when I'm having a bad day. A 'lie flat' option is useful as DS does like to have a kip when we're on the move. The graco wheels are quite small, I was thinking bigger wheels would make it easier to push, but then they would affect how small the fold was, wouldn't they? I guess size isn't quite such an issue as we're about to buy a ford focus instead of our fiat punto, but we only have a little flat and zero space for storage!