I use a case but no screen protector. My case has a small lip on it so if I set it down it's not laying on the glass. Sometimes I don't use a case at all. I have the iPhone 6 plus now and used a iPhone 5 the same way before this. My iPhone 6 plus has 2-3 really small and light scratches on it. You can't see them at all when the screen is on. You can't feel them either unless you drag your nail across the screen. I also work construction and my pockets are always getting dust, sand, or asphalt in them. So for the most part I can't complain about the screen scratching easily. I don't keep anything else in my pocket with my phone. I've had the iPhone 6 since it came out and I think the scratches are mostly from work when I get a lot of debris in my pockets. You will lose $50-100 in resale value if you get a couple scratches, but you'll save that by not buying screen protectors. Plus using the phone is a lot better without a screen protector.
Never used a screen protector on any iPhone. Only the iPhone 6 Plus leather case from Apple. Twice I've dropped my phone, but was able to kick it before it landed so it went flying horizontal instead, and was fine. Not scratches at all on my phone. Hate screen protectors.
Case only, no screen protector. I've had a 3, 3gs,5, and 6 and the same set up each time. Never once has a scratch on the screen either. All my drops to the face/ corner were saved by using a case that had a lip over the screen. I religiously keep my phone in my right front pocket with nothing else in that pocket.
I always use a screen protector. But due to the design of the 6's with the rounded edges, there are no screen protectors made that don't stick out like a sore thumb. In the past I would pride myself in getting super installs where you couldn't even tell there was a screen protector.
So for me the options for my Plus are seeing a crappy looking protector all the time or tiny surface scratches that I would have to hold up to a light and really look for. Therefore I go without. I do use a case mostly for better grip and I do have Apple Care.
I used a screen protector for every iPhone i previously had but over the last year starting with the 5s I got to the point where they just started annoying me. Especially with how easy they can get scratched and my OCD goes nuts with making sure it's aligned and has no dust. So a few months into having the 5s I took the screen protector off for good. Same with the 6 Plus, other than trying one out that came with my cases, I've gone naked on the screen. Sure the screen gets those faint micro scratches that are most likely in the oleophobic coating but unless you are looking for them in super bright light, you can't tell.
With my last phone, the GS3, I used a film screen protector for a couple of months, then went without one for the next year and a half. The screen ended up with a couple of very minor marks, none which could be felt or seen with the screen on. Since my iPhone 6 is still only two months old, I'm back to a film screen protector for now. I'm not crazy about how it feels or collects grease, but I feel better knowing that if I want to upgrade to a 6S, I'll have an absolute mint condition 6 to sell.