Accessing nested data properties in Handlebars
Kevin Decker (one of the contributors Handlebars on Github) answered on the GitHub issue I had created.




  The with form will be slightly faster than the generic block form due
  to some optimizations that can be made for known cases like that. You
  also have the option of making pathed lookups, {{amount.preTax}} for
  example. All work and unless you have extremely hot code I wouldn't
  worry too much about the performance of one vs. the other and leave to
  to which feels stylistically the best for you.


So I guess there is no real winner, unless as Kevin points out, you have an extremely used template then with might be a better option.