From personal experience with SD card much easier. Just take the card n put it in a new phone. I had a phone that died on me n data in the phone was inaccessible..but the SD card was intact..so not all data was lost.This phone comes in only 6 GB RAM + 128 GB ROM
So they don't really force customers buy a more expensive version with bigger memory its either customer accept this model with this fixed memory or they don't. I bet some customers really require larger memory so this phone will not be suitable.
I have a habit to clear my photos everyday by sending it to the cloud. Actually for me 16GB is more than sufficient. Also I do not have too many apps.