Answer:
ExpertRank is a relatively new technology brought forward by Ask.com. They claim it is more powerful in deciding the rank of a site in SERP. No doubt there are flaws in Google trademark PageRank. e.g traffic should be one parameter as many consider. According to Ask.com Ranking is not all about the volume of links pointing to a page. They also say that its about the pages expertise on the subject but they don't say how they do it. Definitely its not the only criteria that Google puts into Page rank. There are other factors too. For example relevance of the page forwarding the link, the anchor text and many other such criteria. PageRank technology has played a lead role in deciding a page's rank in Google SERP, bt its not the only criteria too.
So as long as we get relevant search results from our favourite search engine we really don't care if PageRank is better or ExpertRank is better.
As for now PageRank rules.Mmay be in near future ExpertRank will come into the big scene too.