Rome is the best fit in my opinion. Consider:
Wikipedia states: “Many Biblical scholars believe that ‘Babylon’ is a metaphor for the pagan Roman Empire at the time it persecuted Christians, before the Edict of Milan in 313. . . Perhaps specifically referencing some aspect of Rome’s rule (brutality, greed, paganism). . . In 4 Ezra, 2 Baruch, and the Sibylline Oracles, ‘Babylon’ is a cryptic name for Rome. Reinhard Feldmeier speculates that ‘Babylon’ is used to refer to Rome in 1 Peter 5:13. In Revelation 17:9 it is said that she sits on ‘seven mountains,’ typically understood as the seven hills of Rome. A Roman coin minted under the Emperor Vespasian (ca. 70 AD) depicts Rome as a woman sitting on seven hills.”
According to the International Standard Bible Encyclopedia: “The characteristics ascribed to this Babylon apply to Rome rather than to any other city of that age: (a) as ruling over the kings of the earth (Revelation 17:18); (b) as sitting on seven mountains (Revelation 17:9); (c) as the center of the world’s merchandise (Revelation 18:3, 11–13); (d) as the corrupter of the nations (Revelation 17:2; 18:3; 19:2); (e) as the persecutor of the saints (Revelation 17:6).”
According to Eusebius of Caesarea, Babylon would be Rome or the Roman Empire: “And Peter makes mention of Mark in his first epistle which they say that he wrote in Rome itself, as is indicated by him, when he calls the city, by a figure, Babylon, as he does in the following words: ‘The church that is at Babylon, elected together with you, salutes you; and so does Marcus my son (1 Peter 5:13).'”