The
Graco Snugride is a basic, relatively low-cost favorite for many techs & advocates -- fits newborns well, installs in most vehicles well + it's pretty easy to use.... Just make sure that it's the front adjust version (having to fix the harness strap from the back is a real hassle & more often leads to misuse unless parents very diligent).
The
Graco SafeSeat Step1 also fits newborns well, but also fits bigger babies longer so although it might cost more up front, it ends up being quite cost effective in the long term. It is also easy to use & fits most vehicles very well. You don't have to carry baby in it all the time, but being able to keep the seat at room temp longer is a nice comfort option in extreme climates. Plus, you can keep spare bases installed in alternate vehicles to make rides with Grandma or whoever that much easier & in an emergency it can be used without a base.
However, the
Marathon would probably fit 9+ pound newborns fine (mine didn't fit until about 4-6 months old, though)