I tried to put emphasis on the personal nature of the question in the title. I’m not asking for myself or the average individual. I also mean ideal in the way where cost is still a factor. The iPhone 16 Pro has a 1TB model but it’s around $500 more expensive than the 128GB version.
I imagine answers are going to vary significantly depending on an individuals approach like relying on cloud storage, SD cards, or a Magsafe NVMe drive for example.
I found 1TB (512GB on the phone and on the SD card) was ideal for me. I could keep the things I wanted for “just in case scenarios” like the files needed for the source ports of Diablo, Half Life, and Morrowind in case I want to play a game or some ebooks if I have time to read. I never needed to uninstall applications and shuffle things. I even had plenty of breathing room.
Another question I’d be interested in hearing people’s answers to is what is the minimum storage capacity you would consider for a phone. I don’t think I would buy a device with less than 256GB of potential storage. If it has an SD card slot that opens up the potential a significantly.
Ideally, 256 GB + microSD. 128 GB today gives me ample room for my offline maps, music collection, podcasts, and Kiwix libraries. No gaming, only the occasional video, and one photo per day on average, so 256 GB would future-proof it.
As for a minimum, 32GB. For several years, I had a phone with 4GB of internal storage. Didn’t use the microSD slot since it seemed to drain the battery. Android takes up much more space nowadays, but I wouldn’t be too upset having ~16 GB usable space for myself.
The SD card would be separately encrypted as a portable backup of everything important to me, accessible on-the-spot whenever I need it.