Multiple Car Seat recommendation needed

[denna]

First off what is the safest infant seat currently on the market?
I havent had to buy an infant seat since 2005 as I re-used DS1's infant seat (Britax Companion) with DD. I LOVED my Companion but it expired last Fall. My favorite part was the inflated headrest which I just noticed the Chaperone does not have. Do the new flaps provide as much support? Is there an infant seat on the market that does have a nice insert like the Companion had?
2nd question is for spare seats for Grandma's car. My mom just moved in with us and will be caring for the kids (part-time) while Im in school. Id like to get spare seats for her cars (which may double in the future as travel seats). Which spare seats do I buy? Current stats:

DS1 is in a Britax Frontier. He is 4 years (5 in April). 43" and 40lbs
DD is RF'ing in a Britax Boulevard. She is 18 months (2 in July). 34" and 28lbs. Id prefer to keep her RF'ing as long as possible but honestly she will not be in my mom's car that often. Its mostly for DS dropoff/pickup. And Im sure that is all. If there is a less expensive (than Britax) seat that RFs just as long thatd be great.

Thanks so much!