I've had my 6+ Since they were released and I've gone with no cover to keep the size down and it's still in very good condition, I read the gorilla glass is very hard to scratch, I do try to ensure that when ever I put the phone in my pocket that there are not coins or keys in my pocket that could scratch it. I have one or two fine scratch marks on the apple logo on the rear other wise the back is still in marked
I am using my Iphone 6+ without a case. I dropped it soon after getting it and got a small scratch on the screen. You can't see it unless you look for it. The 6+ is kind of slippery so you need to be careful to pick it up with a positive grip.
I'm not a big fan of cases for normal use. They make the phone bigger and gunk accumulates under the case and causes scratching and damage to the phone. My old phone (3GS) lasted much better without a case. Part of the appeal of the Iphone 6 is that it is such a beautiful object. It would be a pity to ugly it up with a case.
I am on the lookout for a decent case for times when I do need that protection. Still looking.
Got a "Survivor" case. Yep, sure it's bulky but it still fits in my pocket (albeit took some getting used to) Have dropped it on its corner twice - no damage. The case back is made of rubber so it grips to surfaces and never slides off