A.V.
I personally think our Marathon is worth every penny. If you want a particular brand, I'd focus just on that brand and then compare what you need between models. We went with the Marathon in part because it would go from 35RF and 65FF and that was pretty high for the time (now they are 40 and 70). My DD is short, so we didn't need something that would fit a very tall child, and it would fit in my car. I also had friends who were very happy with their Marathons. I don't know if any Graco seat has a RF tether, which was another reason we went with Britax. We bought two (different times, online and on sale) and we mostly leave them in the cars she rides in most. Occasionally we'll install them somewhere else or move the one out of the van to move furniture or something when we don't need her seat. I find the adjustments to the straps to be very easy and the covers are very washable. If you have LATCH, installation is even easier. I figure by the time she's 65 lbs, we'll be looking at a booster/the new laws anyway. She is going to be 3 this summer and still RF and while she does kick the back of the seat, she's not uncomfortable.
We also had a Keyfit 30 and were happy with the transition to the Britax. We also bought on albeebaby.com.