Congratulations on the upcoming arrival of your first child! You've been getting some good information so far, but I just wanted to add my $.02. You should contact the hospital where you are planning to have your child. They will have trained technicians who will help you with the proper installation before your child ever leaves the hospital.
Having previously been one of the certified child restraint technicians, I will add that the best place to install any child restraint device is where it can best be installed/secured in the vehicle. Since our seats are relatively flat, any of the rear locations should be fine, from there it comes down to personal preference. Rear seats with center humps are not usually a good location.
At one time, the center rear position was recommended for the best protection against side intrusion during a crash (look both ways before entering an intersection even when your light is green). The main things to consider are proper angle (many devices have a type of level indicator on the side) and proper securement. As previously mentioned, once properly installed, there should be very little side to side movement (less than one inch). You should be able to rock your vehicle by pulling side to side on the safety seat. If you end up using the seat belt, be sure to install the locking clip!
Your owners manual and the instructions that come with a child restraint are also good sources, but most people are too impatient to read them all, and they can be confusing at first. Another source for good information is
Safe Kids Worldwide . They provide safety seat information and checkpoints where you can have your devices checked for proper installation and recalls.
For a bit of humor: As a defensive driving instructor for more than 22 years I was often asked where is the safest place to install the seat. Back when the center rear position was the recommended location one parent asked, "What if you have more than one child?" One of the other students in the class chimed in by saying, "You put your favorite one in the center rear position!"
Finally, use the bed of your truck for carrying cargo. Any objects being hauled in the passenger area can become deadly to you and you passengers during a crash...even groceries.
You will soon find you have a new purpose in life! Congratulations!