I've had some experience with each. I first bought an iphone & then switched to Android after an iphone update ruined the phone. Spouse owns a Windows Phone. Here are the pluses & negatives I've found with each.
iPhone pluses: easy to learn & navigate, itunes, lots of apps
Cons: expensive!, can't customize anything, slow at times, lost ALL audio output after automatic update with no remedy, camera & display was lacking for the price I paid when compared to other unlocked phones
Android pluses: you can customize pretty much anything, great prices for unlocked phones/value, lots of apps, fast OS, syncs well with laptop
Cons: lags at times with certain apps (could be the apps fault & not Android)
Windows phone pluses: inexpensive/value, fastest & best OS I've experienced in a phone by far, camera in Lumia phones, Cortana, keyboard
Cons: lack of apps
If Windows Phone gets more apps, then the smartphone battle is over.