I was wondering that myself. I have an iPhone X 256GB with the battery starting to get old that I am going to trade in. . . My usage of the memory is not that great. I figure I will get the same size. I store most of my pictures on iCloud to share with my other Apple devices and I dont use any music. YMMV. However, the screen display size on the iPhone 11 Pro Max is much higher density than the iPhone X, so that may make a difference. Buying on time makes only a $6 difference per month in price over 24 months through Apple. Not a big deal.
I have the XS Max, 512 GB. Currently I am using 133.6 GB of the 512.
I have almost 50,000 photos and 1050 videos @ only 9.14 GB because I store my photos in iCloud. This is also great for me to sync across all my Apple devices.
I have almost 8,000 songs at 48 GB, I never delete text strings w/images so I have 33 GB Messages, and I have several thousand emails (LOL) on three email accounts. I know, embarrassing I need to do a lot of email maintenance!
So I hope that helps you have an idea how you might utilize a certain size iPhone.
I am an amateur photographer and could not wait for the XS Max. That screen is incredible and the camera is amazing! I will say Im a tiny woman so I have noticed lately some hand strain because I have small hands. I went from a 6S to the XS Max and the width difference was noticeable, and I use my iPhone naked, only utilizing a Sena leather pouch - wonderful, btw.
So for you, Yaelle, that may be something to think about too. Most people use a case which will add a little more to its already larger width. I have a way Im working around this however and Im not sure I can part with this size screen now.
I do not like the look of the new iPhone 11 Pro, just the camera esthetically so I dont know if Im going to sell this phone and upgrade. I may wait another year hoping for more advancements. Also, I am going to watch a lot of YouTube people to get hands on reviews.
I admit Im trapped, quite willingly, in the Apple eco system. I dont want out. These devices are not only fun to use they are life enhancing. I was so struck by the health benefits of Apple Watch I am seriously going to check out the new Series 5. Impressive in so many ways what it can do to save lives and even tell you to breathe and calm down. Yeah, Im a woman but I dont mind if Apple tells me that. Haha. Hope this helps a little. Its only my experience so far.