Having the idea to code a “project” probably means a lot of lines of code at the end.
In this case, TS is generally better because it allows to avoid many errors by type checking at the code generation step.
Agree with @jerome
100% Typescript! especially if you are using ES6 packages
Doing that you will be sure to use correctly all the babylonjs classes and features before compiling!
EDIT: You will also have autocomplete OMG