Minions' Base Attack Critical Strike Chance is equal to the Critical Strike Chance of your Main Hand Weapon: Overrides your minions' base critical strike chance. Sources of additional critical strike chance (e.g. Increased Critical Strikes Support, Assassin's Mark, Brittle) still apply to this new value. This weapon can be held in the off hand to allow a different main hand weapon to be used.
Slayer's Overwhelm notable Base critical strike chance for attacks with weapons is 8% does not interact with Sandstorm Visage: a spell will use the weapon's base critical strike chance even with this notable allocated.
Maata's Teaching itself is a great main-hand option due to having a high critical strike chance roll on a high critical strike chance base type. Very few other unique one-handed melee weapons have a higher critical strike chance.
Augyre provides the highest possible base critical strike chance, but provides no other stats useful for minions. Combined with a (Divergent quality) Rallying Cry, it can add a sizable amount of additional physical damage - approximately 100 without any warcry buff effect.
Actum only grants 5% base critical strike chance.
Local critical strike chance implicit modifiers (e.g. from corruption) or the Harvest enchantment that grants 1% increased Critical Strike Chance per 4% Quality may be useful to maximize the efficiency of this modifers.