L.R.
I have had 2 Expeditions, and a Britax Marathon has held both my children in them perfectly. The car seat began as my daughter's, but when my son got too big for his infant seat, I gave him the marathon and got her a seat that can go 5 point harness until 100 lbs. I can say that the marathan is a preferable seat beacuse it is comfortable and doesn't cause any problems when my children fall asleep in it. My daughter's seat now causes some seriously painful-looking head tilts when she falls asleep, but my son looks so serene. My husband is a firefighter and is very concerned with safety and he has always been a fan of the Marathon. Good luck!