how easily does the screen on the apple watch series 7 stainless steel graphite scratch?

I agree with lobsterghost1; I've had stainless since my very first watch and have never had a glass scratching or cracking issue. One the other hand, my family members have aluminum, and have had experiences with cracked glass.

Is it the different crystal? Maybe, maybe not - but I'm not willing to experiment with an aluminum case to find out. :)

Every stainless steel watch has a sapphire crystal, so it's not easy to scratch at all, unlike the aluminum watches, which have a different composition screen (iON-X). My Series 4 in Stainless never scratched. I've had my Series 7 now for a couple weeks and it's pristine. This is one of the very good reasons to spend more money on a stainless watch.

I'm now on my 3rd Apple Watch and have ONLY purchased Stainless for the durability of the sapphire screen and stainless case itself is stronger than aluminum. They cost more, for a reason.