I have a Honda Fit and we're starting to look into purchasing a convertible car seat for my car. LO is almost six months old and getting heavier, so lugging around the infant car seat is getting cumbersome. My question is, what convertible car seat is best for a smaller car? I've looked at both the Britax Marathon but I've also heard good things about Diono. Any suggestions or votes for one or the other would be great. TIA!