The Roundabout is the most basic car seat. It is really meant for babies from five to 35 pounds rear facing or forward facing up to 40 pounds and a max of 40 inches. So, this one isn’t for a larger child because it will not get quite as much versatility out of it.
Next in the line is the Diplomat. The Diplomat is a little bit of an upgraded version of the Roundabout seat, but the idea behind it is that it’s meant to fit compact cars, such as sporty cars are or some coupes. Again, maximum of 40 pounds and can also be rear facing or forward facing. However this model is a more compact version. And it really is smaller when compared to other models from their line.
Than comes the Marathon. It is probably one of the most popular models (and I’m not talking only about Britax), partly because of its price but also because it goes up to amazing 65 pounds. So, you do get to go rear facing from 5 to 35 pounds and you also get to go forward facing from 20 to 65 pounds.

The Decathalon is also goes up to 65 pounds, but it has a couple of added features that Marathon doesn’t have. It has a toddler pillow and an infant positioning system. These can both be removed as baby ages, so this is a great option for a growing child.
And last, but not the least - the Boulevard features true side impact protection and also goes up to 65 pounds. It is a super luxurious seat – definitely the highest end product on the line. One of the great things about the whole Britax Line is that they all feature a tangle free harness and one hand adjustment. That just makes is so much easier to get your precious child in and out of the harness. You do not have to worry about the harness.
And if you have a better idea of which car seat would be better for your child, please leave a comment.