Kydex?
Buy Brown (David Brown), Mashed Cat, Azwelke, Okuden, are the only ones I have personally used. I would not hesitate to recommend any of them.
For leather, I am a bit poorer on recommendations. I have owned Armoralleather (leatherman to some, I believe), held Chuddybear, Mikeymoto, , Paul Long (a real master, who goes out of his way to give advice to people like me, making their own leather sheaths).
Honestly, I make my own leather sheaths, so I don't have as much experience with them.
All are great, some may have longer wait times than others, so do some research.