After looking through MacRumors and Reddit for recommendations two months ago I ended up going with the brand Skinomi (search for them on Amazon, they have a bunch of different options depending on what model you have). They're not the best quality screen protector in the world, but they're cheap and sold in 6 packs. Since they're a wet install screen protector they form fit pretty well to the curves of the Apple Watch's front glass. Fairly easy to install and unintrusive. After two months of usage it looks like one of my corners may be starting to peel up, but I'm not worried since (again) it was cheap and it came with replacements. I also think the peeling is due to a minor install error on my part.
I'm fairly satisfied. I would probably buy it again.