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!

[denna]

I have the Evenflo Tribute and Graco Nautillus in my cart right now (Amazon) I really want to keep DS in a 5pt harness booster.

Is this a sufficient pick?

I still really need help with an infant seat. Thanks.

[Joolsplus2]

Sorry, didn't mean to leave you hanging!
Measuring your dd from her bum to the top of her head, sitting against the wall or in her current RF seat, will be the best way to figure out growing room in the Tribute, which is about 22 inches tall, I think (and you want that one inch above her head for RF).
Evenflo Maestro is also a fine choice for the older kiddo, if the Nautilus happens to be a budget-buster.
Chaperone probably has even better head protection than the Companion, as Britax continually refines it's testing and design, but honestly the Chicco Key Fit is an excellent choice, too...SO easy to use, and very safe.(unless you also crave the B-Ready stroller, which I would, that might be excuse enough to go with the Chaperone :D).