When to use each one
Knife-When your lanes are heavily pushing
When your lanes are heavily pushing, ganking becomes incredibly hard unless you have the skill to pull off tower dives, so what you do to help your team since you will be ganking less is get stalkers blade to give your team deap wrds in the enemy jungle so they know when the jungler is near so they can back off in time
Blade-When you plan on heavy ganking
You don't really play this for the damage, you play it for the slow, when you plan on heavily ganking, every bit of cc counts, throw it down on the person u plan on killing.
Saber- Late game dueling
Saber is when you are playing a duelist like xin or master yi, you use it by jumping onto the carry, smiteing them, greatly reduce the dps they offer and you will win the trade