Let or Var in modern javascript?

"Let allows you to declare variables that are limited in scope to the block, statement, or expression on which it is used. This is unlike the var keyword, which defines a variable globally, or locally to an entire function regardless of block scope." - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let

Which one should be used in modern javascript code? let or var?

Edit:
I checked the Google JavaScript Style Guide and it states "Declarations with var: Always" (https://google.github.io/styleguide/javascriptguide.xml)

But in the tutorial at javascript.info (not sure if this is an official JavaScript website or not) it says to use let (https://javascript.info/variables)

I'm assuming I should stick to what Google recommends, but am still open to answers.

Second Edit: The above is not the most recent Google JavaScript Style Guide. In that one it states: "Declare all local variables with either const or let. Use const by default, unless a variable needs to be reassigned. The var keyword must not be used".(https://google.github.io/styleguide/jsguide.html#features-local-variable-declarations)