This answer is long bc I give a set for both forms.
Urshifu (Rapid Strike)
Item: Assault Vest
Nature: Adamant/Jolly
Ability: Unseen Fist
EV spread: 252 Attack / 252 Speed / 4 Sp. Def.
Moveset:
-Close Combat
-Surging Strikes
-Iron Head
-U-Turn
Since you're running only attack moves, you can use the assault vest to give it a special defense boost. Close Combat is it's strongest stab fighting type move. Surging strikes effectively has a base power of 56.25 with each hit because of stab and guaranteed crits each giving it a 50% increase. It also always hits three times, effectively giving it a power of 168.75 (correct me if my math is wrong). Iron Head gives it fairy coverage and flinch chance. U-Turn gives it grass and psychic coverage, and you can also use it to reset the stat drops caused by Close Combat.
Urshifu (Single Strike)
Item: Assault Vest
Nature: Adamant/Jolly
Ability: Unseen Fist
EV spread: 252 Attack / 252 Speed / 4 Sp. Def
Moveset:
-Wicked Blow
-Close Combat
-Iron Head
-Thunder Punch / Ice Punch / Zen Headbutt
Like Rapid Strike form, this Urshifu hits as fast and hard as possible EV wise. Assault Vest is important for giving it a special defense boost. Close Combat for fighting stab. Wicked Blow is its strongest dark type move, with effectively a power of 180 due to stab and guaranteed crits (again, correct me if I'm wrong). Iron Head gives crucial fairy coverage. You can then choose Thunder/Ice Punch for flying coverage, or Zen Headbutt or fighting coverage, so take your pick. Also they are all contact moves so they benefit from unseen fist (which is why I chose the punches over Stone Edge, also they are 100% accurate).