hey,
So crit and lethality are both good although most high-elo or pro players go lethality since it gives you more burst damage which is what shaco needs most imo
Crit is also a good stat ofc it's better if you think you will be able to stick to the target longer and land several autos but lethality gives you a stronger burst dmg and allows to OS a squichy basically (your first auto will always crit since you use Q and attack from the back)
This is why I build some crit in my anti-tank build since I don't target the same enemies and don't fight in the same way