Other than OBA/yellowing issue, what qualities are important to you in a matte paper?
Surface appearance texture, maximum achievable optical density (blackness) on the particular printer, color gamut on the particular printer, and how well it feeds in the particular printer.
Some people are really interested in thickness / stiffness / tactile qualities. Some people really care about cotton versus alpha cellulose base.
How are you deciding which matte paper to use in which circumstances?
I have pretty much decided that Canson Rag Photographique is my favorite matte paper (usually in the 210 gsm version, which is both cheaper and feeds easier, but there's the 310 gsm version too), but Canon PM-101 Pro Premium Matte is pretty good and much cheaper. So between these two it's cost versus quality for the particular print.