[Zach3794]

Flowmaster is gonna be your general mass produced exhaust, similar to borla. Greddy is Greddy, standard JDM stuff.

In terms of performance, you're not going to notice much of anything with a catback. Period. Your biggest performance gains are going to be from replacing the header and over/frontpipe.

As far as headers that totally comes to personal preference...UEL vs EL. UEL will give you more of a rumble, EL will be smooth.
*EL headers will generally also give much better performance. If you're planning on going forced induction down the line, (turbo), fa20club and P&L both make modular headers which can be converted to turbo manifolds for their respective turbo kits down the line.