In the past few years, Apple and Google have emerged as the two undisputed leaders of mobile. Their combined operating systems have a 99.6% market share. Considering that some countries have up to 80% smartphone usage, the number of these devices is in the billions.
Though there are some other options, such as Windows phone, the lack of market share means that there are fewer apps in their ecosystem. It's a chicken and the egg type problem; people don't have these devices because developers don't release apps for them, because people don't have these devices.
Apps are the real power behind smartphones, and the fewer apps a platform has, the less desirable it is. That killer app you love? Most likely it's only available on Android and/or iOS. Most developers will release their apps for both of these platforms, but some things come out exclusively.
So the question remains, which one of these is best for you? There are a lot of factors to be considered that separate these two offerings. Each excelled in certain areas, but as time goes on most of the major differences are shrinking. In the end it will largely come down to personal taste.
Generally, a high-end phone is overkill for everyday uses. If the most strenuous thing you are planning on using you phone for is navigation, then it's likely a mid or even low-range device will be enough for you. High-end devices will run everything more smoothly, and be more capable of multitasking, but you need to consider the extra expense.
One of the only exceptions here is demanding games, especially 3d ones. If you are planning on doing a lot of gaming on your device you will want to consider the higher end options. The issue with iPhone is there is no such thing as a low-end device. Apples release only high-end level devices, wheras with android there is much more choice for you to pick something closer to your needs.
On both platforms the user interface is generally fairly easy once you've got the basics of using a touch screen. The majority of interactions are fairly similar across both platforms: you tap apps to launch them; drag down from the top of the screen to see notifications and settings. The main difference between them is that more things can be customized on Android.
Android offers much more than iOS in the way of system options and customization. You can even go as far as replacing the version of android on the device with a custom one, although this is not recommended for beginners.
With iOS what you see is what you got. If you don't like the style or how the OS works then tough. On Android you can put widgets on your home pages, hide app icons, and change the majority of the system apps to alternatives. All of this is locked down on iOS.
Though it is true that system updates on iOS are more universally adapted, this is only part of the story.
Apple controls all the hardware and iOS in such a way that they can practically guarantee that updates will roll out quickly to a vast majority of supported devices. This is harder on Android since a host of third party hardware developers create custom versions for their devices. There are very few devices released with "Vanilla" android.
Google has developed a way to mitigate this update fatigue. Their approach is to take all of the system apps, such as the phone dialer, messaging app, and even large parts of the core interface, and separate them from the OS. This means that they can be regularly updated without the need for a total OS update.
When comparing a high end android phone to an iPhone, there is usually little difference in the actual hardware specifications. In recent times the iPhone set itself apart with a superior camera, however releases like Google's Pixel have put this into dispute. The best thing to do when considering buying a new device is to get your hands on it and try out some of the things you are likely to use it for. Most retailers will be happy to demo a device's features. Keep in mind though that they are likely to push you toward a more expensive device, even if it's not required for your needs.
Generally with iOS you are paying a large premium for the brand alone. There are similar Android alternatives at sometimes half the price.
There is also a much wider range of Android options, starting from under $100
It pays to do your research before you even step foot in a shop, or open an online retailer's site. Consider what your needs are, try out the different options and make an informed decision.