Of the persons acquiring liens by virtue of this article and solely for determining priorities as among such persons, laborers, artisans, mechanics, workmen and furnishers of material, machinery and other necessary equipment, shall have first liens, and the lien of such persons, when perfected and preserved as required by this article, shall take precedence over any lien taken or to be taken by the contractor or subcontractor indebted to them for labor, material, machinery or other equipment, to the extent of the amount of the lien of such contractor or subcontractor, and the lien of a subcontractor shall take precedence over any lien taken or to be taken by a contractor indebted to him upon his subcontract, to the extent of the amount of the lien of such contractor, and every assignment or transfer by any such head contractor of his contract with the owner or by any such subcontractor of his contract with the contractor, or any proceeding in attachment or otherwise against such head contractor or subcontractor, with the purpose of encumbering or subjecting his interest in such contract, shall be subject and subordinate to the liens of all such subcontractors, laborers, workmen, artisans, materialmen and furnishers of machinery and other necessary equipment who shall perfect their liens according to the provisions of this article. But all of such perfected liens of such laborers and workmen and of such materialmen and furnishers of machinery and of such contractors and subcontractors, respectively, shall be of equal dignity without priority among themselves, except as otherwise provided in this article.