Should I get a 16GB or 128GB iPhone?

Depends on what your needs are.

If you like having your iTunes Digital HD movies on there, your entire music library, you are a avid photographer and film recorder, huge mobile app game player etc then I would consider the 128GB model.

When I had my iPhone 5, I got the 32GB model, and I never came close to filling it up. I took tons of pictures and videos, but I only kept maybe 1 movie on it, and all the social media apps and rarely any mobile games (not a fan of mobile gaming as much) and I still had plenty of space.

I constantly was updating, adding and removing content on my phone so I never really had a problem with space.

But if you are the hardcore user, and I mean HARDCORE like, wanting to have 10 movies on your phone, 15,000 songs, takes about 200 pictures and videos a day, etc, I think the 128GB model would be ok. But im sure some "hardcore" users dont even fill up a 64GB, as they are contantly backing up on their laptops etc.

All in all, I think 16GB is too small, in todays standards, that would fill up rather quick. 128GB is a bit overkill, but if you have the money, why not!

Personally I think the 64GB is the best one, plenty of space, cheaper and you can invest that money into buying a Apple Watch too!