If you ask anyone what their favorite of something is, they always have a reason. "It fits my style." "It tastes the best to me.", etc. It's all relative and based on opinions. It's the same with technology. With technology, it really boils down to the experience.
Experience is basically your reaction to how the devices work, look, and feel when doing day to day things on them. Do you enjoy checking Facebook and email on your device? Why or why not? Is it frustrating or does it take too long? This could vary from device to device.
Apple is the king of friendly user experiences. Their minimalistic approach is a great factor in why people love their products. In a recent study, iPhone users use their device more often than Android users. People have a better experience using the iPhone so they are more likely to use it. The more simple and eye-pleasing it is to do routine tasks, the more enjoyable it is to use those products more often. This is why I love Apple products. Not only do they all sync with one another, they look, feel, and work better than other products I've seen or used. That could be relative though.
Having multiple devices could change that very point. Let's say you have an iPhone and you love it a lot and it's your primary device for everything. You are thinking about buying a new laptop or desktop computer and aren't sure on what to buy. You've heard about Mac and how good it is but it's a foreign concept to you than that old Dell desktop with Windows XP you've had since 2002. You'd rather stick with the thing you're familiar with, right? Well why not go with the computer that is going to best suit an iPhone user?
This of course could play out with many different combinations. If you have an Android phone and are looking for a new computer, it really wouldn't affect your decision as much. If you have a Mac and are wanting a new smartphone, why not go with the same brand? Of course tablets factor into this as well.
So the bottom line is, all devices have a certain user experience and it's all based on whether or not you enjoy those experiences. If you use an Android smartphone, I won't judge you just because the iPhone serves my needs better. If it serves your needs and you enjoy it then that's all that matters. If it doesn't, maybe you should look into what experience you really enjoy the most.
It's All About The Experience