It all really depends AlsoSulfate. A larger pool of Pokemon work really well with Shadow Claw, while a really small pool of Pokemon benefit from Shadow Sneak. But really Shadow Claw is probably the better move. It has a higher chance of dishing out a critical hit and it's base power is solid, although as far as priority moves go I'd rank Shadow Sneak just below Mach Punch and ExtremeSpeed if that makes you feel better.
In my opinion I'd say you're better off with a Dark Type move as opposed to a Ghost Type move though, but in the case of Aegislash Shadow Sneak is perfect (because no go dark bro for aegislash backlash not the best to give night slash).
