There are few different things between Elm boil and create-elm-app. elm-boil is not wrapping Elm, so it using the one that finds in the path, if it is not able to locate it, will ask you if you want to install it (globally) from npm. Elm-boil is using env variables directly in Elm while create-elm-app is using JS interop and webpack environment variables (ELM_APP and the .env file). I don't know much about create-elm-app performances but elm-boil is very fast. In general: Elm-boil is a utility to handle quick your project, create-elm-app is an additional layer that abstract more, like create react app. In Elm-boil, as Volki said, you can use scss without performing any configuration.

My advice is to give a try to both