Having a big scratch on your phone is like having an itch in your brain you just can't reach. Plus, it lowers the resale value of the device when you want to upgrade. A screen protector can keep the surface pristine, but buying one is more complicated than it should be. It's also worth asking if modern phones even need one anymore.
Do I Really Need a Screen Protector?
The glass on your gadgets has gotten a lot more scratch-resistant since the days of the iPod; however this doesn’t make it not scratch able if rubbed by keys or coins. If you look at any phone kept for a long time around you will see scratches that likely came from sand and other particles with hard minerals in them, like quartz and topaz. Any object harder than your screen will scratch it. So yes, your screen can still be scratched, and it's probably the sand in your pocket or bag that's causing it.
Screen protectors are not perfect even the best ones are usually between a 7 and 8 on the Mohs scale, which is slightly better than Gorilla Glass—but they allow you to pop your phone in your pocket without worrying. Then, if and when the protector gets scratched, you can replace it, keeping the actual screen in pristine condition for a later resale. Screen protectors don't have the self-healing abilities of other protection methods, but they're tougher in terms of scratch and drop-protection, and these days they are pretty inexpensive and easily replicable.
So what is best for my phone?
That said, screen protection is just one piece of the puzzle. These films will help you avoid scratches and provide some impact protection, but if you're worried about dropping your phone, get a case. A screen protector will not protect the back of your phone, the edges, or even the corners of the screen. A good case (especially one with a "lip" over the screen) will do more for drops than any screen protector, so unless you feel lucky, get a case along with whatever screen protection you decide on.
A case will also absorb impact damage much better than a screen protector otherwise would. This is why you mix them both as the screen protector is very scratch resistant so protects your screen from abrasive damage, however could structurally weaken and become compromised when exposed to large amounts of impact damage that a case would be able to absorb much easier. Cases can also be water resistant and even water proof for people who are worried about their phones while near bodies of water. Both screens and cases are easily replaced and fairly cheap, especially compared to replacing an entire phone, particularly if that phone is a ‘flagship’. Making them and ideal protective measure as they can be customised by colour and preference. Just be sure to search for your model phone when buying a screen protector to ensure a good fit to better serve as protection for your phone.