There are a lot of points that you can stick to your mind when choosing a phone. Firstly, iOS is easier to get used to but Android comes with more options. If you are confused between IOS and Android phones, you can pick an iPhone if you hope to get something that is easier to use and updates software fast. If you want more hardware options and look for more affordable phones, go with Android.
Secondly, you had better remember not to pay more than you need on a phone. It is undeniable that iPhone 8, Galaxy S8 and other premium phones starting around 700 dollars and more are attractive options, there are less expensive unlocked phones below 500 dollars which are also great as well.
The next feature to take into consideration is the size screen. You should think only about a screen smaller that 5.5 inches if one-hand use is what you need or if you have small hands. In case you want to see videos or play games regularly, take a phone with bigger screen. Currently, phone manufacturers are making phones with big screens.
Regarding to the display, color quality and brightness are more important than resolution. A 4K screen on a phone is attractive to enjoy but kind of overkill. In this case, you should focus on how bright the display is so it would be easier for you to use the phone outdoors or how colorful the panel is. Remember that AMOLED panels work better than LCD.
You also should not pay too much attention to camera megapixels. It is better to focus on specs such as aperture and other points like dual lenses or optical image stabilization. Of course, lower numbers of aperture are better.
Last but not least, the processor is now more important than it was. Even mid-range devices now provide good performance enough for users. However, if you want more power to play games and use augmented reality, you had better opt for an Android device with a Snapdragon 835 processor.