Ranked in these QuestionsQuestion Ranking
Pro Built from the ground up to work with Gulp
Because Slush is built around streams and designed to work best with Gulp. It allows you to get the benefits of a streaming build system without having to manage the components yourself.
Pro Easier to maintain scaffolding through code
Because Slush is built on Gulp which puts code before configuration, scaffolding can be done in a simpler more straightforward way. Creating scaffolding through configuration requires more knowledge about the scaffold's specific implementation and remembering documentation, whereas doing it in code is more self explanatory and requires less domain knowledge to get others up to speed.
Pro Scaffolds are easier to hook up together
Because all Slush scaffolds share the commonality of streams, it's easier to combine them through that common interface. With configuration based workflow wrappers, different components may have specific implementations that can cause problems with interoperability. With streams, there's better encapsulation of functionality, making it harder to mess up a scaffold leading to better compatibility.
Pro Interactively set up projects with the Inquirer module
Pro Own 'repository' of different project templates
Slush has a well cataloged collection of scaffolds created for it by the community, providing a large collection of workflows prebuilt for almost any task you might want to perform.
You can view the list of generators here.
Con Still young with few generators available
Slush is still young compared to Yeoman. Although it has quite a few generators made by third parties and it's quite easy to make one yourself. It still has fewer generators than older alternatives.