I still haven’t filled up my 64GB 6S after all these years, so I know 64GB is my sweet spot. It’s even better when Apple set the baseline iPhones to have 64GB.
On my iPad mini 2, on the other hand, I am micro managing its 64GB storage. So for me, 64GB is not enough on iPads, but plenty for a phone, simply because I tend to use more apps and media on my iPad.
If you don’t want to pay iCloud, go for 256GB.