The paper presents a comparative study of the energetic, structural, and elastic properties of carbon nanotubes and composite nanotubes (including BN, BC$_3$, and BC$_2$N) using a non-orthogonal tight-binding formalism. The study predicts that carbon nanotubes have a higher Young modulus than any of the composite nanotubes, with values comparable to those of defect-free graphene sheets. The results are in good agreement with available experimental data. The authors highlight the exceptional mechanical properties of nanotubes, which are crucial for their potential applications in various fields such as atomic-force microscopy, field emitters, nanoscale electronic devices, and hydrogen storage. The study also discusses the structural and elastic properties of different nanotube structures, including their curvature energy and buckling behavior. The findings suggest that graphitic nanotubes are stiffer than composite nanotubes, and the elastic properties of single-wall nanotubes are similar to those of corresponding flat sheets. The study concludes that BN nanotubes, despite having a slightly smaller Young modulus, remain highly stiff and electrically insulating, making them suitable for applications requiring high strength and electrical insulation.The paper presents a comparative study of the energetic, structural, and elastic properties of carbon nanotubes and composite nanotubes (including BN, BC$_3$, and BC$_2$N) using a non-orthogonal tight-binding formalism. The study predicts that carbon nanotubes have a higher Young modulus than any of the composite nanotubes, with values comparable to those of defect-free graphene sheets. The results are in good agreement with available experimental data. The authors highlight the exceptional mechanical properties of nanotubes, which are crucial for their potential applications in various fields such as atomic-force microscopy, field emitters, nanoscale electronic devices, and hydrogen storage. The study also discusses the structural and elastic properties of different nanotube structures, including their curvature energy and buckling behavior. The findings suggest that graphitic nanotubes are stiffer than composite nanotubes, and the elastic properties of single-wall nanotubes are similar to those of corresponding flat sheets. The study concludes that BN nanotubes, despite having a slightly smaller Young modulus, remain highly stiff and electrically insulating, making them suitable for applications requiring high strength and electrical insulation.