I've been told my old stomping ground (Houston) is extremely competitive. I've not eaten Vietnamese outside of Texas, so I can't really compare. It was shocking to me, when I moved to Portland, OR, to not have easy access to pho, banh mi, and vermicelli dishes. They kinda make up for it with poke bowls?
preface: not of VN extraction, I just like the food.
Houston has excellent Vietnamese cuisine. I guess it's Southern Vietnamese style? (can't help but notice the ARVN veterans memorial on Bellaire Blvd.).
In the East, Falls Church in VA has excellent food. But I think the best would have to be Louisiana. No name places with a shrimp boat out back, on the coast, east of New Orleans. I'm told a lot of Vietnamese refugees were resettled there and went into the fishing industry, southern Louisiana and the Mississippi river delta being somewhat similar to Vietnam.
There are so many Vietnamese restaurants in San Jose it's really more similar to the Hanoi recommendation: you just have to experiment until you find the ones that resonate with your personal tastes. I recommend searching reddit for "best pho in San Jose" -- you'll find a number of threads, many of which feature similar sets of restaurants.