Reputation matters. Companies with the best reputations are often assumed to offer the greatest value to their clients. That’s the conventional wisdom, and on Wall Street, that kind of thinking helped make Goldman Sachs and Morgan Stanley the investment banks with the largest market shares in the mergers and acquisition advisory business. Goldman is even lionized in a newly published book — The Partnership, by Charles Ellis — as the best managed company in American finance. But Alex Edmans , a Wharton finance professor, has found that the conventional wisdom may be wrong. In merger-and-acquisition advice, at least, market share doesn’t seem to equate with value delivered to clients. In a paper titled, “ How Should Acquirers Select Advisors? Persistence in Investment Bank Performance ,” Edmans and Jack Bao, a graduate student at the Massachusetts Institute of Technology, find that market share does not necessarily translate to the best returns for a bank’s clients.…