Britax carseats are the best seats on the market, hands down. We bought the Boulevard for my daughter when she outgrew her infant seat. She is tiny so the infant insert was a great feature for us. I love that I can keep her rear-facing until she weighs 35 pounds.
The Boulevard is a Marathon with True Side Impact added for extra safety. We own both seats and the Boulevard is my favorite seat by far. If you watch for sales, you can get a good deal on a Britax!
My mother in law had this car seat for my son, and was in a fender bender. While my son was in this car seat, he asstained NO INJURYS from it what so ever, while my other son, in a different car seat, asstained whip lash... I wish he would have been in this car seat, then he would not have had any problems! I also love this car seat because its easy to buckle in, you can get it tight without wobbling like most car seats do, and its so easy to clean!!! I highly recommend this car seat to parents and grand parents!
We were looking to get our daughter a new seat. We were told this was the best. I LOVE that you do not have to re-thread the height strap with each growth spurt. You just twish the side knobs and they move up and down getting a perfect fit! The price is a little high but for my childs safety its worth it.
Also, our daughter is on the petite side so the fact that it does from 5-40 lbs is perfect. she will be in it until she is ready for a booster.
Only con I have is the cleaning. I was told you have to take out the straps to get the cover off and You cannot put it in the washing machine.