These have 10% base crit chance and a 1.8x multiplier. Don't waste your time trying to make crit work on these knives, it's just plain bad.

[Spinning Needle] is the best stance for Dual Daggers. It has good multipliers and a very high hit count on its moving combo at a base (before attack speed bonuses) of 5 per second for status spamming.
[Gnashing Payara] has a higher hypothetical potential on its moving block combo but it has too much movement so you're never going to actually land all those hits consistently.

Melee Influence far outperforms any other options.