My first reaction to 12 Pro Max was damn, it's feels heavy and boxy so not a comfortable experience. I'm coming from a 7 Plus. The camera module size and weight adds to this as you can feel the weight shift towards the corner. I was sure this wouldn't be for me so ordered a standard 12 for the lighter weight and aluminium rails.
Now I have them side by side I'm torn. The 12 is nice but the Pro Max feels much more premium. The speakers are much fuller on the Pro Max as well.
I use my iPhone like a tablet so would probably benefit if I learned to adapt to the Pro Max but it is fatiguing to use in one hand. Not sure I like the steel rails as it makes it a little harder on your fingers though. I also think the text/black is a little sharper on the 12 - I think this is because the Pro Max screen shifts to blue/green very quickly while the 12 shifts a little to red so there is clearly a big display difference for me.
In previous years I've struggled with the PWM and have been unable to keep any of the OLED iPhones. This year's feels much better but I can still feel some eye strain but the effect is much less with the Pro Max compared to the 12 so this may seal the deal.