What is a good PSA/Slab sleeve brand?

That’s only if you don’t put them on right. Hold the sides of case as you slide the sleeve on, not the front and back. That’s why 95% of graded cards have those damn vertical scratches, because people hold the front and back when they put it on. Hold the sides and you’re good.

I have superior fit for years and I’ve never had an issue with scratches doing it this way.