What sheets to buy
Other than the smooth PEI sheet that comes with the MK4, what other sheets are people buying and for what filament? I assume the smooth PEI covers all the filaments (PLA, PETG, ABS, ASA, Flex, HIPS, PA, PVA, PC, PP, CPE, PVB, NGEN, composites and more).
RE: What sheets to buy
That depends on you personal preferences for the surface aspect of the model face resting on the print sheet. Each type produces another visual aspect. You should also check on the materials table which sheet type is best for a certain filament and if it needs a special treatment (e.g. glue) for your type of filament.
RE: What sheets to buy
I only print PETG and PLA. I have a satin sheet from my MK3S days. I've been using that for PETG and PLA on the MK4 and it works perfectly. I like the texture that you get from the textured sheet, and I might get one someday soon. I'm not a fan of the smooth sheet.