Based on factors like User friendly, Ample no. free apps, Fast in Response, Bug Free, Stable for long time... you can decide the OS best suited for you.
Come to one by one...
Eventhough Andriod initial versions are with bugs, but latest versions become stable and user friendly... but it still makes the device slow after a certain period of usage. As the uninstalled apps or some processes still running in the background eating your processor performance and RAM which won't show by it. By considering available apps and user friendliness andriod wins the race.
Considering Windows, eventhough it is more responsive and eats less usage, it carries lot of complaints with it. it can't compete with the apps in andriod and also user friendliness.
Considering iOS, it is the stable and more responsive, even after long time of usage device performance can't be affected. So it is the Best considering the response, Bug free and stable ness. But still it can't compete the Andriod in app store.
So it is upto one on which factor he gives more weightage decides his best OS.