I'm an information security professional and will not use Android on the basis of what I know of the state of malware development and deployment for Android. Couple that with the fact that security patches and OS upgrades can be delayed by both the phone manufacturer AND the wireless carrier, and you could be left vulnerable for months or longer. When there is a security issue with iOS, the patch is available to every device owner rapidly.
Once you get past the security issue, it really is a matter of price and preference. I prefer iOS devices to everything I've seen in the Android world. I greatly prefer the iPhone's screen to the Samsung's, for example. I find the Samsung screen to be oversaturated and cartoon-like. I won't say that Samsung is BAD, however.. Just not my preference.
I firmly believe in using the right tool for the job. I use Windows on the desktop (price/performance/flexibility) and am comfortable with taking the steps required to mitigate viruses and other malware. I use a triple-headed monitor setup and don't even want to know how much it would cost to set this up in a Mac context. That being said, the Macbook Air is one of my favorite laptops ever. However, work gave me a Lenovo Yoga and I like that quite a bit.
I will generally agree that Apple's integrated design of the hardware and software produces a more stable and consistent platform - and makes things much easier for app developers - which is why you generally see apps come out for iOS before Android. Device fragmentation in Android also plays a role here. However, the fact that Android is open-source is not the real issue behind the spread of malware. Google's more lax attitude in checking what goes into the Play store is more responsible for that. Another recent example:
Data-Stealing Malicious Apps Found in Google Play Store - it is essentially unheard of to find malware in the Apple App Store because they vet the apps much more rigidly.
So use what you prefer and can afford.. I have a hard time understanding anyone who says, "I will never use _______" and believes that everyone should feel the same way. I may never use Android, but I'm not going to tell you that you're wrong for doing so. (See: Ford vs. Chevy).