https://www.pewresearch.org/global/2015/06/23/1-americas-global-image/
America’s image is mostly positive among the Asian nations polled. Particularly large majorities see the U.S. favorably in the Philippines (92%), South Korea (84%) and Vietnam (77%).
It's from 2015 but more recent polls have found similar data IIRC
https://www.brookings.edu/articles/comparing-global-views-of-the-united-states-and-china-during-the-trump-and-biden-administrations/
79% of people polled in Vietnam chose the US in the "Preferred alignment choice in U.S.-China rivalry" which is a different metric obviously but still points towards the same idea
Edit: According to Luna Oi, Pew Research Center is a neoliberal think tank that cannot be trusted on anything about Vietnam
https://youtu.be/hPCoDz_CPCc
As a Vietnamese I would go with Luna explain that the questions were most likely biased and the results were pulled out from the ass of a hardcore liberal.
However, the PRC wasn't on friendly term with Vietnam after the Sino Soviet split. Alongside border skirmishes and proxy war with China in Cambodia, Vietnamese people felt pretty betrayed when China normalize relationship with the USA and developed so fast while we were still under sanctioned by the US and have no more helps when the ussr collapsed. Furthermore, the South China Sea dispute have certainly been an issue that keeps flashing up the resentments from before and made many Vietnam have a much lower opinion about China and Chinese people.
To modern Vietnamese, the USA is the far away enemy of our next door frienemy which makes them a good opportunistic Ally on paper. Furthermore, America's propaganda is so much better than anyone else, which makes a lot of people even in Vietnam have some false images of the USA. At least they don't have as much propaganda from China to improve their reputation, yet