My vote is for the Roman Empire.Although through raw strength,China can raise large armies,the problem is that the Han regular army is quite small in peacetime,less than fifty thousand IIRC.That's compared to a strength of 400,000 for the regular Roman army.
EDIT:The Roman Empire is definitely better in 1 CE.The Roman Empire has Augustus.Meanwhile,the Han is under of infant emperors under the guidance of the incompetence Wang Mang.