I seriously need help picking a car seat.

I've been doing a ton of research of car seats, and have have been leaning towards the chicco key fit bravo travel system but every time I go to buy it I second guess my choice. I feel like I should get a convertible one to save money in the long run, but then always go back to the chicco key fit Infant seat. I understand the difference between convertible vs infant
But can someone give me some pros/cons for these to help me decide?  Or if you have one that you picked instead of he chicco key fit can you tell me why?