I have alternated just about every upgrade since it was an option. 6 non plus -> 8 plus -> 11 pro max -> 13 pro -> 15 pro max. The battery life on the 13 pro was not fantastic, the 15 pm has been ok but overheating and odd phantom drain has been an issue. Battery life is a big factor for me and two handed texting is much easier on the max. I have an apple leather MagSafe wallet and otter box symmetry case on the 15 pm and one handed browsing works well in my use case (bottom edge of the phone in the palm leather wallet for grip. Yes, you can’t reach the top corners without reachability if you don’t have massive hand, but I feel you can get to most everything with the “windshield wiper,” radius of your thumb.
Unfortunately the only way to figure it out is to try it. Before the higher end features were on the max but now that’s not an issue so it really does come down to size and battery life.
One thing to note that sounds overblown but actually has some merit: the pro line especially has always been heavy (the 15 onward less so), but the weight difference is not as much as you’d expect between the pro and pro max. Reviewers saying the max feels more balanced does actually feel true because the weight is spread over a much larger device. The 13 pro always felt like a small brick to me for what it’s worth.
Leaning towards 16 pm for the battery alone- will see if the added few mm height makes a big difference. Weight diff is negligible at 12g increase or thereabouts.
Also: if you use earbuds for long phone calls or scroll often on a flat surface, the size difference obviously does not matter in those cases.