I absolutely love MintKeeper Matte sleeves; they're the perfect thickness, they're reliable and they're very competitively priced.
The only issue I have is one of supply; they seem to go out of stock quite often and for reasonably long periods, meaning I have to switch to sleeves from competitors when they're not available.
This is a real shame, as I'd use MintKeeper sleeves exclusively if they were always available!