The M103 six in the 300SE/300SEL is repeatedly singled out as the connoisseur's everyday choice: bulletproof, more economical, free of the V8 timing-chain worry, and happy to rev, with a numerically lower rear-end ratio that keeps it from feeling slow. V8 fans counter with the effortless torque of the 420/500/560, so the split is largely a use-case preference rather than a reliability dispute.
M103 straight-six (300SE/SEL) versus the V8s
Mercedes-Benz S-Class (W126) · mechanical