Jenni to be honest the pram, car. Seat option all depends on life style. For example, if you use 2 cars and eat out often, I would recommend both a fixed and a carry out. The fixed you will have to move to at 9 kg anyway and we found it better for long journeys.
The carrying is a good option if you don't want to wake the young baby in the early days transferring car to pram or eating out. For example the baby won't be comfy in a high chair until a good 6 months so eating out you can carry them in.
Also the carry out ones get very heavy, very quickly. I could only really carry it any distance up to Bout 3 months and I'm very fit. ( or so I am told
!
Also you can only leave a baby in car seat 2 hours max unless they lie flat.
Think about space, ease of use and speed , putting a new born in a pram with out weather is a race against time.
All my mates who go travel systems bar the bugaboo have switched to mclaren type buggies now.