"best" is relative and when it comes to exhaust..seems to also be one of very personal taste, which really defines what is best.
As for flow (ie: performance), hard to beat the factory system.
As for sound, well its pretty much general consensus that dodge did it best in making them far too quiet.
cheap mod would be to drop in a mid-muffler delete or rear resonator delete, (dont do both) depending on how much drone you can live with. there are kits easily available for both delete options. a word of caution with the V6 models, they can begin to sound "tinny" (like a ricer) with the wrong one.
Full cat back get costly and to be honest, you may see no real gain in anything, flow or sound..but again, everyones ears, preference and barrier to entry is different.
best advice is to go actually listen to other cars in person, see what you like and what you dont.