I did the whole deal on the exhaust with the single muffler. Perfect for my taste, slightly noticable until you get on it, then it sounds amazing, but not to loud. After alittle over a month I've noticed it got slightly louder, but I don't drive the truck all the time so I'm not expecting it to get louder til many months down the road.

And I had that funky smell for like 3 weeks.

From what I've heard:
single magnaflow - quietest
dual magnaflow - loud
bassani - very loud

add long tubes and everything get noticably louder and better sounding with the excpetion of the Bassani, that one will just put 'fear of v8 god' into any one around

 

I have the Magnaflow 14468 (the louder one) and I am very pleased with the sound. Definately louder than stock, especially when you plant the pedal! You can hear it echoing off of buildings so I know it's pretty loud from the outside!

I have never heard the 14568, but I do know they are quieter.