Every 12 to 18 months I polish mine (stainless steel variants only) with jewellers-grade compound and a basic Dremel-like power tool. I decided to hand down my Stainless Steel S7 and gave it touch up and documented my stages for others: Apple Watch Dialux Polishing
What's fun at the moment is I downgraded to an old Aluminium Series while I wait for my next one to ship. What a difference going backwards! I love the aluminium at the gym, but I will forever be a fan of the raw stainless steel variants for this reason.
I never use a case, I work in the trades and wear this into the salty ocean and gym pools very often. If my watches can survive your's can too.
I think the Stainless Steel is the best, but I love the aluminium at the moment. There's no bad options really, but if you own a raw stainless steel version, you might want to check out my before and afters:
(There's no affiliate links here, just sharing my process as an FYI for other owners).
Dialux Polished S5 & S7
The ability to sell them to Android users.