How do I choose an I-beam?

Could you please elaborate on the process of selecting an I-beam? Could you guide me on the key factors to consider while making this choice? Should I prioritize the material, the size, or the load capacity? How do I determine the appropriate span for my intended use? Would the environmental conditions in which the beam will be used play a role in my decision? Also, how important is it to consider the cost-effectiveness of the beam? Could you provide some tips on how to ensure the structural integrity and safety of the beam? Finally, are there any specific brands or manufacturers that you would recommend for reliable and durable I-beams?