Malware was more prevalent a few years back, biggest case I remember is when someone stole the full Guitar Hero World Tour app, made it free and loaded it with a ton of malware. There are still thousands upon thousands of apps in the play store that have malware though. I believe it was around 42,000 last year.
I have phones from all different OSes myself. I have a 5S, a 1520, a 1020, a Moto X, a Nokia N9, an HTC HD2 which boots like a half dozen OSes, a Jolla Phone and will soon have a Z10 as Groupon had them very cheap. That's what I have at present, I've had way too many phones to speak of and from the G1 was a pretty big fandroid. Worshipped it up to the Dell Streak which is when I got my hands on Windows Phone which I thought I hated til I went back to Android... Missed having Netflix on a phone, missed Xbox live integration, missed the lag-free experience, missed real social networking integration in an OS... I went back quick and since then, haven't really had any reason to go back. Nokia was icing on the cake since I think most will agree that they make some truly premium devices. There was even a thread on iMore not long ago with people talking about how they wanted their OS on Nokia phones.