In the post-pandemic landscape, airlines must advance their fleet planning and strategy to tackle market volatility. Optimizing aircraft selection for specific routes can minimize costs and maximize profits. However, current research lacks route-level demand predictions considering both cost and aircraft attributes. Addressing this, we introduce a novel Aircraft Type-specific Demand Forecasting Model (ATDFM) that determines the best aircraft combinations per route, balancing costs and revenue. The ATDFM estimates demand for various aircraft on China's key routes, factoring in socio-economic and competitive elements. Initial scenarios show a high demand for Airbus's large single-aisle aircraft in China's main market, assuming their procurement cost doesn't exceed a 3% increase in operating costs, with Boeing's medium single-aisle jets following closely. Airbus performs well on international routes, while Boeing shines on regional and non-hub journeys. The study bridges gaps in the existing literature by focusing on route-level analysis and incorporating thorough assessments of operational costs and economic efficiency, while multi-scenario analysis yields insights into how different factors influence the selection of optimal aircraft types. The findings aid airlines in refining aircraft purchasing and flight operation strategies, while also assisting suppliers with strategic planning for product design and production line layouts.