Según vengo viendo la métrica mas acertada en este momento es el MozRank, a continuación dejo una reseña en ingles a ver que les parece:
"Everyone in the SEO world knows about PageRank: the higher your PageRank, the more authoritative Google perceives you to be on the whole. SEOmoz has developed a number of tools that are comparable to PageRank, such as their MozRank and MozTrust metrics. The best of SEOmoz’s metrics are combined into one simple and easy-to-use metric: Domain Authority.
Domain Authority is scored on a scale of 1 to 100. The higher your score, the more authoritative your site and the higher you can be expected to rank on a Google search. This metric has become so popular, so easy-to-use, and so accurate that many are beginning to believe that SEOmoz’s Domain Authority is a better predictor of your standings with Google than PageRank itself. Whether you buy into this idea or not, Domain Authority’s larger scale (0 to 100 rather than PageRank’s 0 to 10) allows you to see greater nuance when comparing the authority of one site vs. another."