This being said what is the correct equipment to use both ranged and melee to achieve a critical hit using the ninja?
Its like the question which tire is best for a car on race track X under weather conditions Y,
the answer depends on more than the factors given by the ninja.
For ranged attacks its either death stars or throwing stilettos,
the latter give you a higher crit chance,
with the disadvantages of less avg damage, no chance to poison for 15 hp/turn
and 2.5 times the weight of a death star, which is pretty important if you throw up to 18 times/turn
(the max number of swings and attacks each turn is somewhat random,
and influenced by characters stamina lvl and last not least the weapons weight)
For high lvl & HP targets where we have no big chance to instakill
I prefer the shuriken to work on both options,
i.e. hoping for the crit and maximizing dmg in case it wont happen.
The disadvantage of less range can be mitigated, see below.
For close combat attacks its probably martial arts,
more flexibility, max swings/turn without dual wielding penalties,
but disadvantage of higher stamina consumption than e.g. the stiletto, and only close range.
In early to mid game the dread spear from 2nd row is also a good option for its extended range
and the +20 skill bonus contributes to chance to hit and therefore also to crit.
The additional advantage of martial arts for ninjas is the option to switch between 3 weapons:
By default you must spend a turn to swap weapons etc from pc or party inventory
but thats not true for ammo or thrown weapons in personal inventory,
you can swap them at any time without spending a turn.
This allows to e.g. have a spear equipped and use the other slots for either mA or shuriken
respectively go with sling for long range attacks (if the others in party are rangers)
and change between MA and shuriken in the other slots.