When comparing Semaphore CI vs Snap CI, the Slant community recommends Semaphore CI for most people. In the question“What are the best hosted continuous integration services?” Semaphore CI is ranked 7th while Snap CI is ranked 15th. The most important reason people chose Semaphore CI is:
Projects can be imported from GitHub and Semaphore will automatically connect with that repository, once that's done, it will automatically trigger for every code commit.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro GitHub integration
Projects can be imported from GitHub and Semaphore will automatically connect with that repository, once that's done, it will automatically trigger for every code commit.
Pro Complete customer support
Semaphore offers all-around customer support for its commercial users.
Pro Free for open source
Semaphore supports open source and offers unlimited open source projects.
Pro Automatic Testing
Whenever a new push is made on GitHub or Bitbucket, Semaphore automatically runs tests on that branch.
Pro Easy to configure
Semaphore is quite easy to configure and work with. It easily integrates with GitHub and a first build is only a few clicks away.
Semaphore is configured using .yaml configuration files which can be added from the web UI. There are a lot of tutorials out there that help developers configure Semaphore to their preference.
Pro Free 100 builds per month for private projects
Semaphore offers 100 builds every month for private projects. This package is free for an unlimited time and offers: free & unlimited deploys, unlimited collaborators and running tests in parallel.
Pro Docker support
Out of the box Docker support. Additionally, Semaphore can cache Docker images by using included docker-cache commands.

Pro Track pipeline stage history
Snap CI keeps the build history of a branch for as long as that branch is active. Once it's deleted or merged it is automatically deleted.
Pro Ability to deploy to multiple environments
Deployments are configured to run in sequence, one after one in the build pipeline. Not every environment is updated on every change, this is especially helpful for example for someone who is testing the application and does not want their environment to change while they are doing it.
Pro Pull request integration
Snap watches for pull requests on a repository that it's building and automatically issues a pipeline, attempts to merge the pull-request and finally run the pipeline.
Pro Easy to get going
Interactive tutorials explain how to set up an configure pipelines quickly and easily.
Sane defaults provided for testing and deployment stages.
Pro Build artifact promotion and propagation
Artifacts are manually generated and propagated through the deployment pipeline.
Pro Simple debugging with Snap shell
Snap offers developers a simple and easy to use tool for debugging their applications. Just by typing snap-shell
on their pipeline configuration they will have the ability to visit their logs page where they can start debugging. The log page shows a command prompt with some help on how to use it.
Pro Excellent support
Very responsive and personal support in addition to automated responders.

Pro Automatically creates pipelines when a branch is pushed on GitHub
Snap watches for any new branch that is created and once it catches one of these new branches, if the master branch is configured for a pipeline it will create a new pipeline around the new branch. Once the branch is deleted or merged with master, the newly created pipeline is deleted by Snap
Pro Manually triggered promotions from one environment to another
Snap's build pipeline guarantees that the exact same set of git commits trigger each stage.
Cons

Con Proprietary with private project for $30/month
Semaphore is not free and nor is it open source. Pricing starts at $29 per month. However, there is a free option for private projects which have less than 100 builds per month and it's free for open source projects.
Con Discontinued
Will end August 1st 2017. See https://blog.snap-ci.com/blog/2017/02/06/2017-02-06-snap-announcement/
Con No gitlab integration for enterprises that dont want to use github
Not sure when this is planned.

Con No BitBucket integration
They only support GitHub at the moment. Although BitBucket support may be added in the future.