I am thinking PR69. The strike is absolutely perfect, and the condition is immaculate. The only possible issue I see would be the MD at the base of the Monticello building.
Definitely NOT a business strike. The Mint struck so many nickels for business use in 1964 that in general the MS coins grade 63 or 64. It was quantity over quality.
If I learn just one thing at CT per day, this would be today's thing. Wonder why no one guessed PR70. (Asking out of ignorance not contention.)
It looks dang near perfect. But PCGS has only graded 7 as PF70 with a value of $625. Almost 600 as PF69 at a fraction of that price.
For this date that grade isn't common. Plus, there are very few known toners graded PR 70 (I saw only one within the last year).