1. Are there any statistics showing the ratio of security issues between Android and iOS?
2. What's the most common phone among security researchers?
To be honest, I'm wary of believing this, but I own a Nexus and if I had to give the benefit of the doubt to either Google or Apple, it would most certainly be Apple because they don't make business out of my data (or, not as much as Google, at least).
Not sure about which phone Schneier uses, but he argues that having a smartphone is a logical choice in today's society. However he also brings a nuance to that: that we have the pragmatic choice of leaving our smartphone at home instead of taking it with us, and that we should consider that.
Keep in mind a dumbphone also has big brother capabilities. Just likely less precise/severe (assuming no remote holes).
You can look at the CVEs reported on each platform though and the number of critical vulns is comparable at this point.
I sometimes wonder what would happen if I were to create a new Google identity and start fresh. Would they try to re-establish my old email's profile and data to the new one without my consent?
Probably a dumbphone, so neither Android nor iOS...