I wouldn't say the "Best" but it's not bad. Flat sixes I find downright sexy be they in a Porsche or a Honda Goldwing Motorcyle. Inlines aren't bad either. Your neighbor undoubtedly did not have a stock exhaust on that thing as stock Porsche's are not Loud to the point of being extremely noticeable...Go to Fabspeed's site for clips on their systems. The old air cooled motors sounded particularly snarly when exhausted...Kinda like grabbing a pair of alley cats by the tail and swinging them around over your head..
My Stillen has a nice tone, but certainly not loud...add the HFC's and it'll be louder but it won't sound like a tricked out Porsche (ever)...