Keep the standard downpipes for as long as possible, or basically until they disintegrate.
The bike wizard who tweaks my bike on the dyno has always said the same, he reckons they are way superior to any aftermarket pipes you can ever buy.
Have a look on YouTube to give you a rough idea on exhaust notes.
From experience and also personal opinion go for something midrange in regards to noise, it WILL drive you bonkers eventually otherwise.
I have a noisy one, and a reasonable one, which i change per mood, but in reality the less noisy end can wins without a doubt.
Changing the end can will more than likely result in the bike needing a carb balance to make it run true, in fact it's a must.