I think it is good to take everyone's advice but as most will say every baby is different and will be happy in different systems etc.
We were furtunately given one of these full systems for free http://www.mamasandpapas.com/product-ultima-9-in-1-x-cel-chassis-linear/260370800/type-i/
Pros: Very handy that the baby can be in the cot bit and wheeled around and then brought in the house if still asleep. Jrn FD actually preferred sleeping in this to the moses basket.
Very handy that the car seat could be dropped on to the wheels too, great if baby is asleep when you get to shopping centre etc.
Glad we had it overall
Cons: Chuffing expensive wouldnt have bought one.
4 wheeler is quite bulky and wont fit in many boots
Baby will quickly out grow the cot.
We then bought one of these http://www.mamasandpapas.com/product-cybex-callisto-pushchair-berry/120458300/type-i/ as we were told by M&P's it would take a Maxi Cosi car seat.
Pros: Light and compact compared to alot of pushchairs.
Can fully recline, great for when Jnr FD wants to sleep
Can fit a cot to it if Jnr FD #2 comes along.
Useable pretty much from birth to 4 yrs ish.
Cons: Not that robust in only one years use the wheels are showing signs of failing!
Doesnt take the Maxi Cosi car seat (ended up get a big discount back off M&P's)
OK ish off road but gravelled paths are about its limits.
We tried a sling thing from about 3 months but Jnr FD hated it and wouldnt go in it.
On the other hand he loved being in a rucksack from about 5 months and we use the rucksack probably more than any thing else now.
IMO travel systems are worth it, certainly with less than 8 month olds, but be careful what you go for, some of the travel system car seats are very badly safety rated.