My anecdotal evidence. I don't baby my watches, they get worn for everything, and often get brushed against something, and in the case of my current one, often get banged against a glass sink which is perilously close to the toilet!
My first series 0, which I had for the best part of 2 years, had to be replaced half way through its life due to a smashed screen after a light brush against a wall. The second one was a year old when I got rid of it, and it had a few marks/dents, and a couple of deep scratches in the screen.
My current S3 is SS (black). After 2 years, it's pristine. Not a mark on the screen, or on the casing.
As always - YMMV, and I think, from talking to my friends, the black SS seems to be less susceptible to noticeable scratches than the silver one. That said, I would not hesitate to buy another SS one. I don't baby it like an expensive watch, and quite frankly, it gets abused (I even wore it while I was servicing my motorbike), yet it's still in the same condition as when I took it out of the box.
I wouldn't say the ION-X is rubbish. I would just say it's more susceptible to cracking on impact or deeper scratches than the SS or above. You pays your money, you make your choices. But, you could effectively upgrade your aluminium twice as often as the SS for the same cost.