There are stories and articles showing cracked sapphire screens. I don't know; I can't discredit them. All I know is I've owned many watches with sapphire screens, and it would take an awful lot to crack/shatter them. My Watch has proven its resilience and toughness a few times (band, too, which I'm even happier about). Then again, it could just be that one awkward fall and BOOM. Then again... again... my watches rarely share the same risk of falling that a phone might.
I've seen videos of cracked screens, though. They never show exactly how the screen cracked (9to5Mac had an article with a decent breakdown), but the only ones I've seen for myself involved some idiot and a hammer on YouTube, and another purposefully performing an exaggerated drop test on Facebook. I have a sneaking suspicion that if I were to drop it, say, in the sink, and it hit just right, it would crack. But so would the Ion-X glass. If that's the same glass they use on iPhones, a 1.5 ft. drop from the couch to the floor is (evidently) fatal.
Scratches? There's no contest. That's my biggest concern, and likeliest damage.
Sunlight? I can't tell a huge difference between the two, after comparing them with a coworkers' while out in the field, but it is there. Not enough for me to be bothered, or give up the scratch resistance of the sapphire screen.