Balerion vs Eto: who would win?

Eto favored — Slight edge (~55%)

Balerion · Game of Thrones · Base

Tier
LOW 7-C, up to HIGH 7-C
Attack Potency
Small Town Level, up to Large Town Level
Speed
Hypersonic
Durability
Small Town Level

Eto · Tokyo Ghoul · Base

Tier
LOW 7-C, up to HIGH 7-C
Attack Potency
Small Town Level, up to Town Level+
Speed
Massively Hypersonic, up to Sub-Relativistic
Durability
Small Town Level, up to Town Level+

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