Here's the deal with exhaust -
-Stainless is slightly better (last longer) than aluminized.
-aftermarket (3.5 or 4 inch) down pipe is less restrictive than stock, do it.
- 5 inch sounds a little "deeper" but dosent give you any benifit over 4 inch.
-Get rid of the cat, it's a huge restriction
-aftermarket mufflers are all a "flow through" design (they are wide open if you look through them) less restrictive than the stock muffler. They quiet the exhaust, but it'll be louder than stock.
-straight pipe (no cat no muffler) is the loudest, not really that loud though
- tips will change the sound of the exhaust a little (think, yelling vs yelling through a cone) but are mostly for looks
- decide if you want aluminized or stainless / cat or no cat / muffler or no muffler / tip or no tip.... then get the cheapest one you can find. That's the best one you can get