Infant car seat vs. convertible?

Denise • married to my best friend and mama to a 4 yr old boy 💙 and 2 yr old girl💗 and pregnant with TWINS due in July 💙💙
Help! FTM and I'm so lost on all these options. It seems like an infant car seat lasts approximately the first year (or less) but a convertible car seat goes from birth to toddler. Or am I mistaken that you can use a convertible car seat for infants? Why get an infant car seat then? What are the pros and cons of each? And any specific brand recommendation. Thanks everyone! All these options can get overwhelming. 

Vote below to see results!