Jenkins is a pretty flexible, complete tool. Especially I love the possibility to configure jobs as a code with Jenkins pipelines.

CircleCI is well suited for small projects where the main task is to run continuous integration as quickly as possible. Travis CI is recommended primarily for open-source projects that need to be tested in different environments.

And for something a bit larger I prefer to use Jenkins because it is possible to make serious system configuration thereby different plugins. In Jenkins, I can change almost anything. But if you want to start the CI chain as soon as possible, Jenkins may not be the right choice.