256 for me. Maxed out my first few iphones (3GS, 4S, 5S). Stuck with 64GB for my 6S plus, which was plenty. Then ran out of space all the time on a 64GB Xs. Jumped to 256 for my 13 Pro because of the ProRes features enabled at that capacity. Use around 130GB of it, so stuck with 256 on my 16 Pro even though external storage is now the answer for hi data rate recording