Well Mat Block is useless outside of double battles, and even though Water Shuriken has priority Waterfall is a better choice. If this is ingame then Water Shuriken is fine and although illogical you could keep mat block just because it's cool. If this is for competitive then I wouldn't use them(unless you're going to be playing doubles then Mat Block is good).
Just a little information that you may not know, but Mat Block doesn't have priority.