It really depends:
In doubles, Mirror Armour is a LOT better, due to the fact that pressure is pretty useless in doubles as Corviknight teams won't have the time to PP stall. Additionally, with all the dynamax moves running around, you can obliviate any stat changes - something which is extremely frequent in doubles.
However, on the other hand, in singles, as Coderine Kiss mentioned, PP stalling with Pressure is also viable.
In doubles, PP stalling barely happens due to the fact that there are two teammates who can work in synergy to take down Corviknight. Additionally, a Pokemon typically won't last more than three turns in doubles unless it decides to dynamax, which can extend its longevity but not by a lot.
However, I'm sure in singles (although I've never played it) that PP stalling can be viable too.
Hope I helped.