Are Software Agencies good as a Software Engineer

Just exploring opportunities at the moment. I'm employed at the moment but want to work on android (most preferred), backend or maybe game tools development.

Currently working on frontend using React which is not my strong point + not 100% interested in it. I've also previously worked at a startup using AngularJS which was alright but used to/prefer Java, C#, Python and similar technologies. I'm thinking about if there's an option for joining a company (I guess it's an agency) that finds work for you and "loans" you out to their clients to complete work on contracts. Thinking something like you work at company A for 6 months, company B 12 months, etc.

If anyone has any experience, advise or recommendations about this, would be great to learn more about.