The Holy Roman Empire was neither holy, Roman or an empire, but it was still a strong power despite its infighting. What were the strongest countries towards the end of the "empire"?
Austria and Prussia. They were the only major powers during this time which were also part of the Holy Roman Empire. Other countries like bavaria, saxony or Hessia were minor powers.
Here is an "indirect" source: The site shows the major armies of the involved countries of the Napoleonic Wars. Two of them (Austria and Prussia) are part of the Holy Roman Empire (HRE). If there were other strong countries within the HRE they would be listed here, also.