I am wondering what type or brand of car seat to buy my 5 mth old son.?

You need to buy a convertible carseat that can be used rear and forward facing. Your son needs to be rear-facing until 20 pounds AND one year of age. Until then his neck and back muscles just aren't strong enough to handle being in a forward facing position (especially in the event of a collision). The two brands that I recommend most are anything Graco or Brittax. If you have a son that's especially tall and thin, go with the Brittax...it's more expensive, but it's worth it if you have a lengthy boy, because they're designed with the long-bodied in mind. If you're on a tight budget, go with Graco.