Durability starts with high quality raw materials and nicely machined components. High quality chromoly steel frame will provide a nice ride for years. Many cyclist love the ride and feel of steel. Steel has great elasticity (can be bent, stretched and still remain strong). The feel of the ride on a steel bike is still a favorite. The slight flexing of the frame creates a "floating" feel. The downside -- rust.
Aluminum is a great choice for cruiser bikes along the coast where humidity and moisture in the air feels salty. Aluminum is corrosion resistant. Aluminum is also light. For this reason, One World Shoppe tries to stock primarily aluminum frame bikes. Make sure the rims are also aluminum alloy and the spokes should be stainless steel.