You are going to get an extremely biased opinion from me as I'm the type of person that buys what they want and nine times out of ten that meets my need many times over.
In this regard it means I always purchase the max capacity Apple offers for the model I'm buying - always. 64GB for the iPhone 5, 128GB for the 6+ and 6s+ and 512GB for the 11 Pro Max, which is my current primary phone.
But I upgrade every 2.5 to 4.5 years. I'm not plunking money down for this every year. I want to have capacity in case I need it, even if I never do. You can't go and get more later on if you need it.
So, that's me. It's your decision though, of course, so go with what you're going to be comfortable getting.
I'll just add one point…my mom once was in the market for a new car. She had a choice between a high-end 1996 Honda Accord with all the options and a 1997 middle of the road Accord with one custom option. Guess what she got? Well, I drive a 1997 Accord I got from my parents.
I heard her regrets about that choice for years.