Re: Roundabout vs Marathon
There really is no "best" brand of car seat. Different seats meet different needs and situations. Britax makes nice seats but they are almost never the first seats I recommend purely because you can get seats with (IMO) better features for less money. So much of choosing a seat is subjective because they all pass the same tests and we don't have the results of the tests so as far as we know, they're all equally safe. Car seat manufacturer marketing departments make all sorts of claims about safety, such as claims about their SIP performance, but they give no data to back those claims up. There are also currently no side impact standards for them to meet.
CPST-I and SAHM to DS