This is almost like asking about religious or political views. Most people today are brain-washed by marketing or simply go with what they've used in the past. There is no right answer, but you should pick based upon your needs.
I *think* the question is about Smartphones.
I use a Nokia Lumia 920 Windows Phone because of access to my data anywhere, great Xbox games, and about 4 times faster than an iPhone and 25% of the cost.
@pyrotics Apple is actually 20 years behind in considering security. Google it and you'll find Windows is the least vulnerable and has been for nearly a decade.
Android currently dominates the market, followed by iOS that is steadily losing ground to Android and Windows. Despite the Pentagon buying an ungodly amount of Blackberrys, RIM is still a dwindling unmentionable.
It'll be interesting to see how all the major players respond to privacy concerns. iPhone has the most market share to lose with apparently Apple supported NSA malware to spy on every iOS user. Microsoft has rolled out free encrypted e-mail for all users and Google has several press releases pending.