This take has been written without taking budget and other shit into consideration.
1. Chipset
We're talking about SoC.
SoC means 'System on Chip's, which means all the components from CPU, GPU, etc to Radio components combined into one chip.
So when you hear terms like Snapdragon 835 SoC, it means that Snapdragon has made a chip by combining the core components. You will come across terms like ARM, Adreno, Tegra, Mali etc.
ARM, like Intel and AMD, produces microprocessors. Adreno is the name of GPU developed Qualcomm. You can research about this stuff if interested. Now, look closely to the chipset specs before buying.
2. Operating Systems
All optimised and no bullshit.
It's important that you do your homework about the provided OS. Most popular are the Android, iOS and windows platforms. The brands will usually tweak it to make it better or worse, the latter is usually true. iOS will keep things simple. But be careful with Android, as the provided one may have annoying bugs. HtC, Samsung, Asus etc have decent interface with minimal bugs. Phones with Cyanogen, MIUI etc will annoy the fuck outta you.
3. Brand
Big brands, big money, but better build.
The Veterans will usually have the best build quality and will have the least hardware issues. My Nokia C6-01 still works fine. However, having good build quality doesn't always mean that your phone will resistant to rupture and elements. The Galaxy Note 7 had an explosion issue. Yes, EXPLOSION. Even the most respected brands can sometimes have very serious issues. So do your homework and talk with someone who is using the same phone.
4. Display and Sound
You don't want a crappy sound and visuals after spending big money.
When talking about the display, there are three things you should keep in mind. The type of screen, the resolution and the screen size. Super AMOLED display is state of the art right now. As for audio, loud doesn't mean good. You will need to check the audio chip and the speakers. And don't forget to hook up the earphones. HtC is known for its twin boom sound.
4. Battery life
Big battery doesn't always mean better endurance.
Multiple factors affect the battery endurance. Don't be surprised if a 4100mAh battery dies and 2800 is still at 30%.
5. Toughness
Never drop your phone.
Check for the screen protection, the water resistance, frame materials, etc.
6. Features
So many phones.....
The Galaxy S8 offers the best features right now. Phones with the same price tag often have a wide feature gap.
7. Other stuff
Like earphone jack, tech support, warranty and other less important things.
Learned a few things? Good.
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