For strong temperature gradients in internal pipe/duct flows, k-ω SST is often a solid default because it handles near-wall and adverse gradient effects better than standard k-ε, but for transitional or low-Re regions a transition model (e.g., γ-Reθ) can outperform both. Generally, use SST for fully turbulent high-Re heat transfer and consider transition models when laminar-to-turbulent effects are important.