Metamorpho vs Jiji: who would win?

Metamorpho favored — Slight edge (~55%)

Metamorpho · DC · Base

Tier
9-A, up to HIGH 6-B
Attack Potency
Small Building Level+, up to Large Country Level
Speed
Relativistic+
Durability
Small Building Level+

Jiji · Dandadan · Accessing Ki

Tier
9-A, up to HIGH 8-C
Attack Potency
Small Building Level+, up to Building Level+
Speed
Superhuman
Durability
Building Level

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