exactly the same, except for the muffler, whether or not it has a resonator, pipe size, type of metal used, bending method used...
all that being said, it is really up to you, pick which sound you like. if you are worried about cops, get something resonated.
if you are looking for something to last a long time, dont get aluminized steel.
there is a post somewhere in this section that has videos of alot of the exhausts out there, or get on google videos and start watching