"best" is subjective. One person might say x is the best, while another person will say y is the best. Unfortunately, videos don't do justice of how it sounds in person.
Here is few picks that I like and ran on my cars.
1.
Borla Sport Exhaust - way too expensive now.. sounds great with headers and zero drone.
2.
Eisenmann E46 Performance Exhaust -> Race Exhaust 70mm Tips -> Paired with a Vibrant Ultra Quiet Resonator. (
retained the front muffler).
best tone zero drone, but needs headers to open it up.
3. Vibrant Street Power Muffler paired with Vibrant Ultra Quiet Resonator (full custom 3" exhaust from headers back).
This was the loudest setup, but sounded incredible but had a smidge of drone.
I think the Eisenmann Setup is the best tone in my honest opinion and cost is probably the best option if your stock exhaust is not rusty. Full E46 exhausts these days are stupid expensive.
--
I have a friend who is running an ISR exhaust and it sounds pretty good..
ISR Performance Series II MBSE Exhaust - BMW E46 Late 325/330 The ALL New ISR Performance Series II MBSE exhaust is an incredibly stylish and aggressive exhaust system at an affordable price. Constructed of high-quality stainless steel, the MBSE utilizes dual 2.5" mid pipes that mate to a...
drifthq.com
Would be a good option as-well, just remember these cars need resonators...
With that said...
If i would get another E46... I'd do Eisenmann Race Muffler again.