We don’t use a single best architecture, we choose the architecture on a per-project basis or stick to the architecture of your choice when you require it.
Our Android engineers stay up to date with Google's official architecture guidelines. We commonly rely on the MVVM and MVI architectures, but sometimes also work with Flux/Redux-like solutions.
When we develop iOS apps, we use different approaches depending on the size and complexity of the project. Some of the methods we commonly employ are MVVM (with or without Rx), VIPER, Clean Swift, or RIBs.