You know you have speakers like Bose, Sony, and Pioneer that you know are good brands to buy from. Then you have the Walmart brand I want to stay away from the Wall-Mart brand equivalent if there is one because I'm new in the car game and I want to use quality parts.
Research and depends on your budget because that will determine on what you can afford and what you can not afford. For example Jun, Mugen-Power, Spoon, Toda, etc. is beyond allot of people budget then you have AEM, Greddy, Skunk2, DCSport, Injen, etc. that allot of people can afford then you have the very cheap budget that from Home Depot, Pep Boys, etc.