Apple has always been excellent as a hardware designer. They actually design their SoC CPUs (starting with the A5) by hand. Since they have the ability of perfectly mating the hardware with their software, they can produce extremely efficient and powerful devices. They're masters at optimization. I've been a longtime user of apple products, and their software is always incredibly refined, clean, and well optimized. Their hardware is also well designed and well manufactured. I rarely have issues with them. iTunes backups are easy, and despite what people say, the lightning connector is far more robust than USB micro.

Android, however, only represents software, and this software must be capable of running on many different hardware variants. This means that it isn't always well optimized, and often manufacturers include "bloatware" that bog down the operating system. Certain manufacturers also run a skin over the base Android system, and each one is customized. So for example, Samsung uses their own, HTC uses another, and Google uses the bone stock version of Android. This added layer is just another thing to add complication.

Given that, Android being open source, is FAR more capable than iOS is and is usually far more feature rich than its Apple counterpart. There are also far more hardware options to accommodate anyone, whereas Apple's choices are simply "Regular sized, or slightly larger."

For my money, Apple is my go-to. iOS does everything I look for in a phone. Nothing more, nothing less. However, power users and tablet users would be far better serviced using an Android device.

While technically possible, the chances are exceedingly rare. To my knowledge, none exist for both iOS and Android platforms that are capable of auto-proliferation (that is, they won't download, and be sent to other devices like viruses do on PCs). In order to get a virus on your device, you'd have to willingly download it and install it.

That being said, Android devices are slightly more vulnerable than iOS devices are given the fact that they can be rooted to allow for more permissions and more access to information.