Far and away, the most frequently asked question I get as a CPST is "What is the best car seat?" The problem is that this impossible to answer without more information.
It is sort of like asking "What is the best kind of shoes?" While there are many people who have strong opinions on their favorite footwear, NO ONE can answer definitively what brand is best without knowing a bit more. The best ski boots in the world would not work so well if you're trying to dance en pointe.
So if you ask me for a car seat recommendation, I'm going to ask you some questions right back. I'm not being nosy - I want to give you the best choices to work for your situation that I can. Also, I will tell you that ALL seats pass the same safety testing in order to be legally sold in the United States. I cannot tell you which seat is the safest because that information is simply not available. Anyone who tries to tell you their seat has the highest safety ratings is misinformed or lying to you. The best seat is the seat that fits your child and vehicle, and is installed and used correctly.
How old is your child?
I will not recommend a forward-facing seat to a child under the age of 2 years old, and I will not offer booster recommendations for a child who is not yet 5. Similarly, a convertible seat is usually not the best choice for a 3-year-old who is already forward facing.
What is his height/weight?
For a child who is tall for his age, I will be sure that my recommendations feature taller harness slots and longer harness straps, whereas that may not be necesssary for a more petite child. For a very small infant, I will offer suggestions that have harness slots that can be used safely.
What vehicle is the seat going in?
Some vehicles do not work well with some car seats. The type of seat belt you have, the length of the buckle stalks, and where the buckles connect near the seat bight are some of the variables that may influence my suggestions. Similarly, there are some vehicle positions that do not play nice with *any* seats, and I may recommend you rethink where you are installing. The Rav-4, for example, has 3 rear seatbelts, but you cannot use all 3 at the same time, so you can only really have 2 rear passengers. Some newer Ford models feature inflatable seatbelts, which many car seat manufacturers don't allow their seats to be installed with at all. Also, if your vehicle has limited space front-to-back, I can give you seat choices that offer more compact installation.
What other rear passengers do you have?
If I know you are trying to fit 3 across, or puzzling 2 seats next to each other, I can find you narrower options.
Are there other features that are a priority for you?
Are you looking specifically for a no-rethread harness? Does your child desparately want arm rests? Do you want a seat that can rear-face to beyond 3 years old?