Which material sounds better for speakers construction? Wood, Ply or MDF?

Aluminum is good material but a) need to be calculated to be low resonant and suitable for loudspeaker b) need dedicated tools, not suitable for DIY c) expEnsive. Natural Wood is good but only with heavy thk. Also need good practice and suitable tools. It is better to use playwood and MDF for DIY being easy to work, less expensive, good acoustic characteristics. It is perfect for final painting or to be dressed by low thk natural wood. In terms of constructability, it is preferable to use playwood for the bottom, front and top side and MDF for remaining panels. Reinforcements by playwood. No problem to glue MDF and playwood togheter as well final layer of natural wood if any. Please to consider that the real sonici part of loudspeaker are drives, crossover, wiring cable (internal and external should be adequate quality and dimensions) as well the cabinet should be heavy, strong, its very low resonance. Have a good DIY

Aluminum? Wouldnt it ring more than the bells of war of 1812 overture?

Yes it would. 

knock on your cast aluminum engine block and tell me how it rings. 

Solid wood, nothing like the real thing. Problems: price, difficult to work and control. But in the end will sound like nothing else. 

For exemple Boenicke builds from solid wood: Cherry, Walnut, Oak and Ashtree. 

IMO the most natural sounding speakers that I ever heard.