Many no longer use PR to evaluate a site's authority as it's no longer being updated and the current PR data being displayed is outdated. Therefore, you should use backlink checkers like ahrefs, majestic seo, and open site explorer. Any of these tools can generate a list of all the backlinks of your competitors they know of and sort them according to their authority in descending order using their proprietary metrics. Ahrefs uses url and domain rank, majestic uses citation and trust flow, open site explorer uses domain authority and page authority. My favourite and the most accurate is Ahrefs. It's also the fastest in discovering new links among them all.
Ahrefs is the best when analyzing a competitor but if you are using a free account then you will only get a limited information.