The veteran centre-back has left Real Madrid after 16 years at the Santiago Bernabeu.
Despite being 35, Ramos is still a capable defender and as such is attracting a number of Europe's biggest clubs.
They include United and PSG, but City's interest is minimal.
Given the option of joining either United or City, Ramos would chose the Red Devils, according to Spanish outlet AS.
Ramos has prioritised United as he values their "history and greatness" in English football.
The report claims PSG have presented Ramos with a financially superior offer compared to their English counterparts.
The World Cup winner also loves the city of Paris, which could be a huge factor in his decision.