Star-Lord (Classic) vs Kamen Rider Buster: who would win?

Star-Lord (Classic) favored — Slight edge (~55%)

Star-Lord (Classic) · Marvel · Base

Tier

9-B, up to 8-A

Attack Potency

Wall Level, up to Multi-City Block Level

Speed

Relativistic, up to Ftl

Durability

Wall Level

Kamen Rider Buster · Kamen Rider · Megid War (1-15)

Tier

9-B, up to 6-C

Attack Potency

Wall Level, up to Island Level

Speed

Massively Hypersonic, up to Massively Hypersonic+

Durability

Wall Level, up to Island Level

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