It depends which one to chose is based on the requirement
Handler is mostly used to switch from other thread to main thread, Handler is attached to a looper on which it post its runnable task in queue.
So If you are already in other thread and switch to main thread then you need handle instead of async task or other thread
If Handler created in other than main thread which is not a looper is will not give error as handle is created the thread, that thread need to be made a lopper
AsyncTask is used to execute code for few seconds which run on background thread and gives its result to main thread
** *AsyncTask Limitations
1. Async Task is not attached to life cycle of activity and it keeps run even if its activity destroyed whereas loader doesn't have this limitation
2. All Async Tasks share the same background thread for execution which also impact the app performance
Thread is used in app for background work also but it doesn't have any call back on main thread.
If requirement suits some threads instead of one thread and which need to give task many times then thread pool executor is better option.Eg Requirement of Image loading from multiple url like glide.
