Here is a list of features to look at when you're shopping to help you decide which infant seat is a good choice for your family:
1) Fit in your car. The most important thing. Try to install the seat in your car. Make sure that the driver and/or passenger can still sit a safe distance away from their own airbags, while leaving an inch of clearance between the infant seat and either front seat. (Very few infant seats allow touching the front seats; you'll have to check the manual to see if yours does.) Can you safely install the seat or the base so it doesn't move more than an inch side-to-side or front-to-back when you grab it where the seatbelt goes through? Does it install at a proper angle, or close enough to adjust with a pool noodle, for the baby? (Too upright can cause infants' airway to be cut off.) How hard is it to get the seat in and out of the car in the position you got a safe install?
2) Weight limit. Usually either 22 or 30 pounds. The smaller seats carry average sized babies until close to a year, the larger usually to 15-18 months. Most infants will outgrow the infant seat by height, not weight. The seat is outgrown by height when there is less than one inch of carseat shell above the baby's head. It can be nice to put off buying a convertible seat for longer, and some people feel like they get more for their money with a longer lasting seat. But by then you'll just be using it as a regular carseat-it's pretty rare that you'd want to carry around a ten pound carseat with a twenty pound baby in it. Some babies also prefer to be more upright by the time they're about a year old.
3) Harness adjustments. You'll be using these constantly, every time you get baby in or out of the seat. I highly recommend picking a seat with the adjustment on the front. It's definitely worth a few extra dollars. Also, seats with just one strap to pull on for adjusting are a LOT easier to use than seats that you have to adjust each side separately.
4) Newborn padding. If you have any reason to suspect you'll have a preemie or very small baby (ie multiples), be sure to pick a seat with plenty of supportive padding for newborns. The Chicco Keyfit is very good for preemies, for example. You want a seat with low harness slots and a sturdy newborn insert.
5) Handle positions in the car. Some carseats allow you to drive with the carry handle in the up position, and some require you to put it all the way down. Leaving it up can save you a few extra inches which can be valuable if the seat is a tight fit in your car.
6) Cost of extra bases. It can be very convenient to just buy a second base to put in DH/Grandma/Babysitter's car, but some bases are very expensive. If you plan to buy additional bases, be sure to factor that into your cost.
7) Extra features. Some seats have levelers in the seat or on the base to help you be sure the seat is installed at a safe angle for the baby, which can be very helpful. Most seats come with sunshades. Some have rigid, alligator-style LATCH clips which are a lot easier to use if that's how you'll be installing the seat in your car.
8 ) History of the seat. Carseats are best to purchase new. Please don't use one from a garage sale/secondhand store/craigslist type of source. There's just no way to be sure the seat is safe for your child. It IS okay to use a seat that you or someone you know and trust has used before. Here's a checklist to make sure that a used seat is still safe for this child: http://www.cpsafety.com/articles/usedseat.aspx
9) Fit with a stroller. A lot of moms really like the travel system idea, being able to pop the infant seat out of the car and right onto the stroller. Many strollers will accommodate other brands of carseats though, so don't feel locked in to a prepackaged set. Experiment with combinations of strollers and carseats you love.
Also, skip all the extra aftermarket products. That includes mirrors, toys to dangle from the seat, extra head cushion inserts, extra padding, different harness strap covers, carseat covers not sold by that manufacturer for that seat, DVD players, vehicle seat protectors, seat belt tighteners, etc. If it didn't come in the box with your carseat, don't use it. It hasn't been tested with your carseat in your vehicle and could pose a safety hazard to your baby in a crash. The safe options are:
1) To protect a seat, lay a thin towel on the vehicle seat before you install the carseat.
2) To add extra head support, roll up receiving blankets and put them on either side of the baby's head AFTER baby has been safely buckled.
3) To correct the angle of installation, use 1-3 cut pool noodles for adjusting the recline. Check the carseat manual before doing this-some require the base to be in the lowest position to use noodles, some allow it to be in any position. If you need more than one noodle, duct tape them together.
4) To get the belt tighter, put weight down in the seat or on the base. Sometimes it helps to have a friend push on the seat or base while you tighten the belt.
About the time you pack your hospital bag, make an appointment with a technician to learn how to be sure your seat is safely installed in the car. It can be very tricky since every seat and every vehicle are different. Over 80% of carseats are installed improperly in the U.S. It will take about half an hour to learn how to get a safe install of your seat-well worth it to be sure your precious baby is protected in the car!