There are two types of car seats you'll have a choice between, an infant seat & a convertible car seat...You're going to need a convertible car seat eventually (you're toddler will use it until they're large enough for a booster seat) so many might reason that you should just spend the money on a convertible but before you decide let me give you my thoughts...
An infant seat is portable, a convertible is not. Meaning that if your baby falls asleep in the car (which he/she will, guaranteed) you can just lift out the infant seat (the seat has a base which remains attached to your seat) & keep them asleep. (fingers crossed) With a convertible car seat you have no choice but to take the baby out of the seat or sit in a parking lot twiddling your thumbs waiting for them to wake up.
The other big bonus of a portable seat is you'll have somewhere to put the baby when you arrive at your destination. Set the infant seat in your shopping cart or keep them in it at a restaurant. In fact many restaurants have infant seat holders called "slings" that you can set the infant seat right into. (much safer than the old upside down highchair trick). Until your baby is old enough to sit in a high chair (around 6-8 months) you'll be stuck holding them or bringing the stroller unless you have an infant seat.
My other reason for endorsing an infant seat is that although newborns can technically ride in a convertible car seat I think they're far too slumpy for it. Newborns are little more than a big blog & that blob has no strength to hold itself up. In an infant seat they're somewhat reclined which although is a bonus for a newborn will also be one of the reasons you'll want to switch your older baby to a convertible seat.
So with that said the choice is yours (obviously).
If you're really tight on money then you might want to only spend the cash once & get a convertible seat. If you can afford to start off with an infant seat & switch to a convertible later than that's the route I'd definitely recommend.
As for brands, I'll give you my two cents on what I've purchased for my girls & then hope you experienced moms will comment with what has/hasn't worked for you with your car seats!
My first car seat was a Chicco Keyfit 30 Infant Car Seat. We bought it because the Chicco Cortina KeyFit 30 Travel Systemwas highly recommended on Consumer Reports. In my next post I'll get into why I HATED my Chicco Cortina stroller but as for the infant seat on it's own I'll say I'm pretty ambivalent. The seat installed easily & I liked that I could buy an extra base for my husband's car & grandma's house. However, I wasn't in love with the amount of padding & texture of the seat's fabric. It wasn't the most inviting for a sensitive little newborn (or my picky design taste) & kind of cheap to be honest. A Hula Moon Car Seat Cover however was an easy fix for both. (China Doll print, SO stinking cute!) The car seat & cover lasted through both of my girls & the Chicco Key Fit 30 continues to be an affordable, Consumer Reports recommended car seat.
When it came time for a convertible seat we once again did our homework on all the different brands as well as checking out the displays in person at my local baby store & finally chose the Britax Boulevard 70 Convertible Car Seat. I love this seat. It's very easy to install, has great padding, super soft fabric & wonderful safety features like side-impact head padding which many other seats haven't yet included. We've done a lot of car seat shopping in this house & I must say I'm a Britax girl through & through. If we ever have another baby (I can sense my husband's nervous twitch from me just typing that) I would probably buy the Britax Chaperone Infant Carrier.