The Britax Marathon (model G4.1) is a top-ranked seat in our Convertible Car Seat Review. It managed a higher than average score in every metric including crash test scores and ease of installation and use. This seat is a soft, comfortable seat that is easy for parents to install and use. It is hard to find anything wrong with this lovely product that also has the easiest to use non-rethread harness height adjustment and ten height positions for maximum adjustability and best fit for children of all sizes. This seat shines in comparison to the competition and is a standout no matter what may be important to you.
The Marathon has been discontinued. Britax is in the process of rolling out a new line called Essentials by Britax and it includes a very similar convertible car seat to the Marathon called the Allegiance (which is less expensive). This may be a good choice for parents who want but can't find a Marathon. they also have the Emblem which is similar as well and also less expensive.