A SaaS offering like Sauce Labs (or BrowserStack or LambdaTest, etc) will provide a remote Selenium/Appium Grid including the ability to run test automation in parallel (up to the amount based your subscription level) an a wide array of browsers and mobile devices.

These tools can be expensive, but if you can afford them, the expertise and effort of maintaining the grid, browser updates, etc. is worth it.

AWS Device Farm can be significantly cheaper, but is much more work to setup and run. It will not give you as many devices, or the reporting and screen/video capture you get with the the services. And there is no support for AWS Device Farm, and very poor documentation. I have used it, but do not recommend it. Running your own grid and physical device lab is better, but I'd stick with a service like Sauce Labs or Perfecto which will save you time and give you better services despite the higher price tag.

Stability - Just works. Availability - More than 15 datacenters. Enterprise features like SSO, local testing and SOC2/GDPR compliant.

BitBar's Dedicated Devices would be a great option for you. It allows you to dedicate (reserve) devices for your use only which also having access to all of the devices in the shared cloud. BitBar has the features and integrations that you are looking for as well.