Benben Tsukumo vs Parry: who would win?

Parry favored — Slight edge (~55%)

Benben Tsukumo · Touhou Project · Nameless Form

Tier
LOW 2-C
Attack Potency
Universe Level+
Speed
Infinite, up to Omnipresent
Durability
Universe Level+

Parry · Dragon Quest · End of Story

Tier
LOW 2-C
Attack Potency
Universe Level+
Speed
Immeasurable
Durability
Universe Level+

A heuristic estimate from normalized VS Battles Wiki stats: tier, attack potency, speed and durability.