Seiichi Samura vs Anguirus Spear: who would win?

Anguirus Spear favored — Slight edge (~55%)

Seiichi Samura · Kagurabachi · Base

Tier
9-A, up to 7-B
Attack Potency
Small Building Level, up to City Level
Speed
Massively Hypersonic+, up to Sub-Relativistic
Durability
Small Building Level, up to City Level

Anguirus Spear · Godzilla · Base

Tier
9-A
Attack Potency
Small Building Level+
Speed
Unknown
Durability
Small Building Level+

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