If I run the same task in each of the coroutines, what would be the difference in time

And I'm wondering how it would work on different devices (different amount of core)

Main uses different scheduling mechanism (on Android it uses Handler to schedule coroutine invocation), so it may be at some point different, but still don't understand what kind performance characteristic is important for you

Because you said about different about of cores, but how this related to task performance? It's more about single core performance and how many parallel tasks you can run and how efficient it will be

So in general I think this is not something coroutines specific and has too many factors to measure it properly

Also, because each of mentioned dispatchers has own use case not sure that it make sense to compare them at all

For example if invoking on Main thread for some reason somehow faster or slower what does it change for you? You anyway cannot block it and use for any blocking IO or CPU intensive task

You added Unconfined to comparasion, but this dispatcher doesn't have any own threads, just run coroutine on your current thread