Vaishnavastra was More Powerful. Its one of the Strongest Celestial weapon along with Brahmashira and Pashupatastra.
Narayanastra was unique weapon. The more you resist, its Power would Increase again and again until it'll kill you.
But it has a serious Drawback., It won't attack Opponents who surrenders to The weapon.
When Ashwathama used Narayanastra, Krishna said to lay down all weapons and surrender in front of That weapon. Thus Narayanastra was Neutralised..
Vaishnavastra doens't have any such drawback. Krishna saved Arjuna from Bhagadatta's weapon. Clearly he was unable to save Himself even though Arjuna Boasted of countering it..
Having been thus pierced and pained, he angrily resorted to the vaishnava weapon. He invoked the mantra on his goad and hurled it towards Pandava’s chest. That weapon was capable of slaying everything and was released by Bhagadatta. Covering Partha, Keshava received it on his own chest. On Keshava’s chest, that weapon became the vaijayanti garland.
Even Krishna says you would've been Toast if I hadn't violated my pledge And Neutralised My weapon(Vaishnavastra).
It was from him that Pragjyotisha obtained this weapon of mine. O venerable one! There is no one in the worlds, not even Indra and Rudra, who cannot be killed by it. It is for your sake that I repulsed the weapon and violated my pledge. O Partha! The great asura has now lost his supreme weapon. Kill him, as I killed Naraka earlier, for the sake of welfare.
It has The Same Hype of Pashupatastra and Brahmashira…
