Car seat for someone who doesn't drive much

So, I'm only 11 weeks and have plenty of time to figure this out but I'm stumped on what kind of car seat to buy.  We live in the city, currently have two cars but rarely drive, maybe once a weekend (or less).  I'm not sure if I should skip the infant car seat and go right to a convertible one.  Can anyone in a similar situation weigh in?  I take public trans and walk most places now.  Maybe I'll want to drive more with a baby?  I just don't want to waste money.