If you buy an Android phone, the key issue is getting software updates from the manufacturer. With Windows in particular, which is the nearest equivalent (one OS on many different hardware devices), MS has a very good system that provides updates to their core operating system for many years after it is first released. This is possible because MS has fairly tight control over the Windows OS, and because the nature of the OS makes it easy to customise for different hardware.
Android is a very different beast, and that creates problems for end users. Typically the stock Android is customised by a hardware manufacturer for their product, and then further customised by the carrier who sells it to the customer. There is a big shoving match as to which of the three is responsible for updates to the software. But the vast bulk of Android devices out there are not able to receive updates for security issues (and Android has had its fair share of exploits). This is because Google can't make an update for the customised Android that the manufacturer has produced for their platform and that in part is due to the nature of Android (and Linux) in respect of the adaption to different hardware platforms. By and large, manufacturers are passing the buck on supporting non-current models of their phones and it is rare to see a version upgrade (compared to the Apple scenario where new iOS versions come out regularly) let alone a guarantee of security fixes for any period of time.
It is for this reason (and a few others) that I have reluctantly concluded that to be sure of getting a phone that will receive a good level of support from the manufacturer for security and version updates, that I will have to spend a little more and buy a Google Nexus. Google makes these phones (and the newer Pixel series) to compete head on with Apple. But the lower end models are still affordable compared with the iPhone (I have many friends who have iPhones and I can't quite bring myself to ask them how they were able to justify the huge expense, since at the time of writing the cheapest new model is $749) - Noel Leeming has an unlocked Nexus 5X for $399. This is really as high as I could justify for a phone, and a long way up from the $149 you could pay for a locked Samsung Galaxy J2 at current pricing (I paid more than that for mine) - $149 is also what I paid for my Lumia 635 and its predecessor.
The Nexus has 32 GB of onboard memory, but there is no microSD card slot, and it also has a USB-C socket, which means different charge cables. There is also a fingerprint sensor for the unlock, and you get a stock Android version in it, so you aren't missing out on features the OEM has chosen not to implement (as I found with Samsung's implementation of Do Not Disturb on my Galaxy). It comes with Android 6 but Google has guaranteed availability of Android 7. So we shall see.
