Oriana Thomson vs Anno Un: who would win?

Oriana Thomson favored — Slight edge (~55%)

Oriana Thomson · Toaru Majutsu no Index · Base

Tier
7-A, up to 6-B
Attack Potency
Mountain Level, up to Country Level
Speed
Sub-Relativistic
Durability
Small Building Level

Anno Un · Undead Unluck · Base

Tier
7-A
Attack Potency
Mountain Level
Speed
Hypersonic+
Durability
Unknown

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