The USSR would span its territories in the 80s but be led by a competent Marxist leninist party. Same for the Warsaw pact countries and Yugoslavia. These were caused by revolutions popping up all across the globe and other areas.
The US choice would have itself devolve into chaos while its power and influence decreases. Infighting would break the US into pieces but territories like hawaii and alaska would gain independence. The main government would be torn asunder and the CIA rogue and unfunded.
USSR all the way. When the US collapses, it won’t be a pretty sight and whoever takes upon himself the monumental task to deal with the various militias and terror groups that will snatch control of high-tech weaponry, will take years and incur massive costs of life and effort in the process of mopping up that shit. It is better to have a single weak US government in place with which a renewed USSR can establish diplomatic ties, continue to trade, and eventually conduct a peaceful and orderly transition into socialism with help from the outside