It is also important to note that you should never use both the LATCH system and the seat belt system at the same time because using both can cause failure in the event of a crash.
|Simple Car Seats Reccomendations for Children from the NHTSA|
Sometimes, I get overwhelmed with all the recommendations and in researching this new law, I found another great and simple resource through the NHTSA site about determining which seat is best for your child. The above graphic is from their site, simple and clear. You can find the full guide here.