316L is a very common stainless for use in watches. We'll have to see about the 'cold forged' bit, and see if it makes a real-world difference in scratch-ability.
I expect the SS Apple Watch to scratch quite easily - I have a couple mirror-polished SS watches, and they scratch readily. The good news is that 90% of the visible scratches are on the bracelet, rather than the watch itself.
Similarly, when the watch itself does get scratched, it tends to be on the bezel or area surrounding the crystal, which is all glass/sapphire on Apple Watch.
Thus, I don't really expect the scratching to be much of an issue. Maybe if you run the side of the watch into a door or something, but otherwise, the sides shouldn't see much wear - bracelet and bezel take 95% of the wear for a normal watch.
Given the wrap-around no-bezel design of the Apple Watch crystal, I'd expect the crystal to take a lot of wear. Unless the Ion-X glass turns out to be amazingly scratch-resistant, this will be a big positive for the models offering Sapphire, especially if you intend to keep the watch a while.
The good news on SS is that it's not very likely to bend, ding or gouge under normal conditions, so you may have some surface scratches, but even in heavy use you probably won't have major damage.
Anodized Aluminum wears very easily, and is prone to scratches, and we'll have to see about the Ion-X glass in the Sport model. The aluminum body will accept scratches, dings, gouges etc. pretty easily, for sure.
My guess is that for many people, the Sport models will look pretty beat up in a year or two - given normal upgrade cycles, that may or may not be a problem.
In response to the person above who mentioned Titanium - titanium is incredibly strong, but it's VERY soft - it scratches like crazy, and I've seen titanium watches that look almost 'melted' after a few years - all the high points are worn down and curved. It's a great material, but not at all scratch-resistant.
My final thought on scratching - the Black SS models are going to be DLC (Diamond-like Carbon) coated, which is fantastic (hard to imagine it not costing extra). DLC coating is *very* scratch-resistant, as it's effectively a coating of little blobs of diamond. If you're worried about scratches, the DLC-coating is the way to go.
The downside is that it can eventually be worn off of high-wear points to show the underlying material, or (more often) knocked off a small section of the steel by an impact. My current DLC-over-SS watch looks perfect, except for one tiny spot on the bezel where the DLC is missing.
I have no info on the Edition materials, so I won't attempt to speak to them at all.
Long story short - the Aluminum models will be by FAR the least durable. It remains to be seen how that plays out and whether it really matters in real life, especially given a probable use-life of just a few years.
The bare SS models should be the most-durable over the long term, but in the middle in terms of scratch-resistance.
The DLC-coated SS models are in the middle for long-term durability - you'll see bare SS in any location the DLC is worn/knocked off - but the best for scratch-resistance.
Again, given the relatively short expected life of an Apple Watch, if the pricing isn't insane, I'll probably be getting a DLC-coated Black SS.
Watch site clearly stated that the Sport does't have a ceramic coating before it was updated. Also you can read this on the 
