An iphone or galaxy is best, i have an iPhone and dropped it a lot of times without a case and it still survived, and its the easiest to use.
I want to buy a new smart phone with all the functionality - so anyone can tell me which device should i buy an iPhone, Android or Windows?
First recommend, Buy iPhone. If you do not have a tight budget thing about Samsung. Otherwise, buy anyone and increase it,s functionality with Android apps.