The Rheem Proterra PROPH50 T2 RH350 leads with a 3.55 UEF and 72-gallon first-hour rating versus the AO Smith Voltex PHPT 50's 3.42 UEF and 67 gallons (per manufacturer data). Rheem adds Wi-Fi while AO Smith stays simpler and often quieter. Choose Rheem for smart-home integration and marginal efficiency gains; pick AO Smith if you prefer straightforward operation and lower noise.