Vietnam exports more (by value) to United States than any other country. It imports more from China and several other countries than it does from the USA.
The WorldBank puts United States as the top market as a buyer from Vietnam, and fifth top market as a seller to Vietnam:
Vietnam top 5 Export and Import partners
The CIA Factbook puts the top export partners as:
United States 23%, China 14%, Japan 8%, South Korea 7% (2019)
However, it doesn't directly reference the source, so it is difficult to trust.
Reuters reported in 2021 that:
China is Vietnam's largest trading partner, on which the Southeast Asian country relies heavily for materials and equipment for its labour-intensive manufacturing. Imports from China rose 30% to $110 billion.
(Note this is based on imports into Vietnam)
The Observatory of Economic Complexity (OEC) provides visuals with the USA as the biggest export market, and China the biggest import market: