I don't know which one is best. I run an aluminium Leovince X3 and I like it. The connecting pipe is made of titanium and the heat shield and mounting hardware are made of carbon fiber. It comes with 4 inserts. two legal, two loud, each with and without spark arrester.
I've had it now for 1500kms and it's still as quiet/loud as it was when new. I've dropped the bike quite a few times and the exhaust still looks ok. Bought it off german Ebay.
Downside? the heatshield could have been longer to protect your inner left leg.