Android is junk no matter how you spin it. Windows, I haven't used that actively since Win2k so can't comment.
It's no less junk than iOS 9. One has flexibility to increase storage, more choice of browser engines, and has a file manager. The other is basically a modern version of Palm OS with a shop to buy stuff.
As for Windows 10, here's the winning levels it achieves over El Capitan:
- a more responsive GUI on a wider range of machines
- support for 32 bit machines
- integrated AI assistant
- a proper Split View that is easy to activate and get out of
- a better faster version of Exposé than Mission Control
- equally good virtual desktops
- up to date OpenGL that is up to 80% faster than El Capitan
- from the current leaked benchmarks it looks like Direct X 12 is twice as fast as Metal on the same hardware and according to Blizzard it supports a wider feature set
- complete admin tool set for everything from managing software and hardware RAID, setting how many CPU cores an application can use, options for display output to 10bit and over, every possible file management option users and admins need
- slightly faster normal boot
- much faster boot from hibernation file
- better support for multiple graphic cards and monitors
- more industrial level apps from companies such as Autodesk
- support for USB 3.1 gen2 out of the box
- kept up to date more often
- updates and betas are tested for much longer time before being released to the public
- better support for legacy apps and games going back many years
- faster video rendering in Premiere and After Effects
- faster CUDA drivers for Nvidia professional use
- better support for next generation displays and virtual reality
- technical support within minutes via web browser that isn't limited to just 90 days or less than a year or at extra costs
Of course some apologist is now going to try to counter the above with some ridiculous reply that could be copied and pasted straight out of some forum in 2000 when OS 9 users were trying to convince themselves they had a better system than NT. Yes, that was a thing that people were dumb enough to believe.