Rails is best for
small to medium sized projects (< 1 million users)
projects that have to iterate a lot
and many other types of projects!
Unless there are good reasons to do otherwise, please use these libraries:
RSpec for unit testing
Authorization using Pundit
Skinny Controllers: they should only receive request data, decode it, and call other layers (models, services) to perform business logic
Skinny Models: they should only represent domain objects (data, relationships between them), validations
Service Layers: any business logic, especially logic that includes more than one model type, should be extracted into a service laye
Use these tools copiously to make your life as a developer easier!
Rubocop: scans for Ruby code smells
Code Climate: scans for code smells
they also provide command-line tools
Brakeman: scans for security issues in Rails
CoffeeLint: lints your CoffeeScript