Good question.
I’d guess:
Sports cat and factory catback to be quietest, then something like a resonated Milltek catback. Resonated Milltek is very quiet. BCS Prestige gets good reviews, not clear if it would be as quiet as the Milltek.
Is it a K03 or K04 car and what are your power and torque goals?
Thanks for that, it’s a Ko3; I don’t have any specific goals on power and torque, but now you’ve got me thinking :-D. I’ve always held that the power of my e46 M3 was just about perfect for UK roads, although could have done with a little more torque. That from memory was around 340bhp and 360nm torque.
Obvs I know this isn’t an M3, so somewhere around 270bhp, 290torque?
When I bought the car a few weeks ago, I was toying between something heavily modified (tried a couple of ed30 highly tuned, the power delivery was quite incredible ) or something strong and standard to mod a little. I opted for the more standard, only because the modded ones, in my price range, were all super high mileage, dubious history or category damaged.