"I have a question for you about car safety.
Living in a big city with excellent public transportation we are very lucky and happy to be able to live without owning a car. We do however from time to time rent a car, go for a ride with car-owning friends or take a taxi and do for these instances need a car seat for our 13-month old son. Even though he is on the small side at 18 pounds and some odd ounces he is outgrowing his infant car seat and we are looking to replace it. And here comes our conundrum: with what? I am at a loss when I try to figure out what kind of seat would suit us best among the plethora of rear-facing seats, forward-facing seats, convertible (into what?) seats, booster seats, seats with bases and seats without bases and so on and so forth. Our number one concern is of course safety, but weight, price and how easy it is to install/uninstall is also important to us."
I'm right there with you in feeling lucky not to have to own a car. But it does make the car seat issue truly tricky, because you can't just install it and leave it in your vehicle.
I am far from an expert on car seats. The two resources I'd highly recommend are The Car Seat Lady and the iVillage Car Seat Message Board. The Car Seat Lady has an extensive website with info about requirements and safety and correct installation. She also does in-person consults in NYC and Baltimore. My favorite thing about her site is that she has more info about using car seats in taxis than you'll find anywhere else, and she specifically mentions the best portable carseat options (such as the Sit 'n' Stroll and the Randian). The iVillage Car Seat message board posters review practically every seat on the market and can give you tips for installing the seat you buy. The thing to remember about the iVillage board is that most of the people posting on it come from the POV of installing in your own family vehicle, so some of the things that they rate highly in a car seat may make it less practical for those of us who use taxis.
A convertible seat is just a seat that you can use rear-facing and then turn it around to use front-facing when the kid is older and bigger. Once your kid is out of the infant seat you won't be dealing with bases anymore, but you also won't be able to wheel your seat around as your stroller (with a few exceptions). It's safer to keep your child rear-facing as long as possible (so if there's no real reason to switch your child at a year you shouldn't do it), and in some countries they have special seats that allow them to keep 2 and 3-year-olds rear-facing. I don't know if those seats come with barf bags.
My data points: I've been very happy with the Graco SnugRide as an infant seat, but I think most infant seats are about the same. The only thing I'd note is that if you're using an infant seat in a taxi, you don't have to install the base first. You can put the shoulder and lap belt through the alternate belt path on the seat itself, so you don't have to lug the base with you. (Just make sure you use the level indicator on the side of the seat so you know when it's at the right angle.) The exception to this is the Peg Perego infant seat, which must be used with the base. This makes the Peg an unwieldy choice for people who use taxis a lot.
We also have a Britax Roundabout. I bought it because a forensic engineer friend of mine bought it for his own kid, saying that the EPS foam would make a big difference in an accident. However, I find it nearly impossible to install snugly in the rear-facing position, and I've never been able to install it to my satisfaction in a taxi. In hindsight, I wish I'd known how tough it would be to install and reinstall it in the rear-facing position, and I most likely would have gone with a different model. My personal opinion is that it's worth the tradeoff of the shock-absorbing foam to be able to keep my kid rear-facing for longer than the bare minimum of 12 months (and to know that the seat was installed correctly before he turned 1). We bought our Roundabout before the Marathon was introduced. My older son was 40 pounds and 40 inches at 2.9, so he was out of the Roundabout long before he turned 4 (the minimum age for a booster). This meant we needed to buy another seat for him anyway before he could go into a booster. So if you're going with a Britax (and yes, the straps are far superior to those on the other brands and that makes more of a difference than you'd think) and your kid has a chance of being tall or heavy or both, I'd go with the Marathon instead of the RA.
Other non-car-owners, what do you think? And do any car owners have insights that would help those of us who need to install and reinstall every time we take a taxi?