i own a new 04 5.4 f150 and was wondering what would be the best exhaust system to install on it for maximum power

ive always had excellent experience with flowmaster...both on my own vehicles and when i worked as a tech installing them...

Flowmaster is a good brand but don't limit yourself shop for what you want and can afford check out http://www.performanceproducts.com/ they have a lot of different types of exhaust systems even complete systems that hang from the original mounts

I have a 2004 Explorer with the 4.0L SOHC motor in it. I am running JBA Headers and JBA exhaust. Sounds great and gave me great MPG. Another thing to take into consideration is your intake. I would get a cold air intake to really open it up to get max. performance.