Answer:
Both the Roman Republic and Roman Empire had periods of instability which ultimately caused their demise. Interestingly, each lasted for almost the same amount of time, so it would be difficult to ascertain one as more "successful" than the other. However, if one considers the extent of the Roman Empire and its continuation from Byzantium after the collapse of the Western Empire, then the Empire was ultimately more successful than the Republic.
Step-by-step explanation: