We recommend gloss.
Graffiti is easier to clean for the average general cleaner off a gloss surface over a matt surface.
However, gloss can affect the appearance of the wall which some people don’t like. If the coating is on a heritage listed building, a matt sacrificial coating is optimal. This will not alter the appearance of the wall.
However, you should check with Heritage Australia before coating any wall.
The new range of Graffiti Eaters Invisible Coatings work extremely well on masonry surfaces and are invisible, without a sheen level at all for property owners who want protection without a noticeable appearance.
These coatings require pressurised water in the removal process.