Convertible car seat+stroller OR travel system?

Kimberly
I'd like thoughts, opinions, cost efficiency on comparing using convertible car seats and a stroller OR travel systems.
     
       We have one family car to use. 
** my first child was only able to be in the carrier car seat of our travel system until he was 9mos before we had to purchase the next level car seat. We had an Eddie Bauer travel system for $200, then the upgraded car seats were an additional $240, until my son is now 6 and in a booster seat.