Android would obviously be the first to get malware, because with Apple you can only install apps from their app store but with Android you can install them from where you like.
Unless you jailbreak your iPhone.
All it takes is common sense, don't install something you're not sure about especially when it doesn't come from a recognised source. Just like with a PC, you follow some strange link that asks for your details or asks you to install something, and you do it, then you're an idiot and you'll get screwed.
Edit: Reworded first sentence, didn't mean to say that I trusted Android more