arXiv is probably the de-facto standard for publishing pre-prints in computer science. The major advantage of arXiv is that its content is included in many other services like academic recommender-systems, search engines, and open access meta-repositories like CORE. Hence, publishing at arXiv ensures a certain level of distribution of your manuscript. arXiv manuscripts are also indexed by Google Scholar.
The downsides of arXiv are that your manuscript is not receiving a DOI and you are not allowed to upload PDF files that are based on LaTeX. In that case you must upload your LaTeX file, which can be very cumbersome on arXiv, especially if you used e.g. Overleaf to write your manuscript.
OSF is the least known pre-print repository of those listed here. However, we like it. It is easy to use, you get a free DOI for your manuscript, and documents are indexed by Google Scholar. Of course, long-term sustainability is a question for this service.
ResearchGate is a commercial service, best known for its academic social network. However, ResearchGate also offers free DOIs for pre-prints.