How long's a piece of string and how deep is your wallet?

You may gain a few bhp at peak rpm on standard jetting with most aftermarket cans but for improved power & response elsewhere, re-jetting is a good investment and will let you get the most out of whichever can you choose.

You won't go wrong with any of the recognised big (and pricey) names.  Value for money and good build quality may also be found with Fuel and MTC Exhausts.  I've seen pretty much every make and model and the only one I would avoid for my own bike is Wolf ... the ones I've seen have looked tatty compared with others of similar price and mileage.

Looks are entirely subjective - what I like, you may not. 

So, no clear winner but equally few that you should ignore.  Beware cheap Chinese stuff on ebay and you'll be OK.