I own an iphone but either iphone or Android is good. I don't know what else is out there but whatever it may be may have more trouble getting support. For example, a few years back Linux Ubuntu introduced a smartphone and I'm sure it would have been great (I wanted one), but none of the carriers wanted to support it, so if there's an issue, you are left by yourself to fix it.
The reason I chosen iphone is one simple reason: I get an acknowledgement when my text goes thru, so if I'm worried about my wife and it says "delivered", at least she's not in the car with her phone at the bottom of a lake somewhere. It has to be working to get a response (she also has the "read" turned on so I know there was a response from her). You can put tracking on either one but I don't want to get into where people are-- just that they are OK. When I text an android, I have no idea if they got it or not or even if their phone is in another dimension until they reply back.
There's no "better" operating system IMO. Android and iphones are based on Linux and Unix respectively, highly secure operating systems free from viruses and worms; as long as you don't deliberately and knowingly download a bad app that can spy or whatever. But that does not happen "by accident". Unlike Microsoft, that seemingly gets malware of all types by no direct user intervention and even by just "turning it on", this day and age where we want security you may want not only your smart phone from one of these two operating systems, but also your home computer/laptop. I already had an android desktop but it's a mobile operating system so it was not meant for a keyboard and monitor, although it will work. Linux is the best for that (and for browser based, a chromebook laptop).