which is the right one to get, 14 or 16?
Unlike previous years, Apple allows you to configure the 14" model with the highest CPU/GPU configuration, so it changes the calculus a little bit.
The 16" should have better battery life and cooling, but it starts at $500 more. And it has "high power" mode, but I doubt many would need it.
This is probably the first time where it comes down to only which size you want to carry around.
Do you find yourself working away from your monitors a lot? Do you move from place to place, or do you set up and not move for a while? How's your eyesight? Do you use the native screen at all while docked?
I find 14" to be good for mostly docked work, or very mobile work. I use reading glasses anyway, so the smaller screen doesn't bother me much, but I find it difficult to side-by-side 2 windows. It's way lighter and fits in almost any bag.
I like the 16" because when working, I use the native screen with my monitors. I don't use this laptop anywhere except in 2 places (home office, and work office). I can definitely fit multiple windows on the screen. I can scale the display up, and it doesn't wind up eating a bunch of my screen real-estate. Apple is quoting more battery life for the 16", so not sure if that factors into your workflow or not.
I never use that even on 40" display. In general where size matters: terminal window is much easier to use if you write long one-liners, reading logs, editing in vim; I do set fonts to be large to have 240x70 characters on the full screen.
Even 16" is too small for any productive work, not mentioning ugly Apple German keyboard layout is absolutely terrible for any serious programming (square and round brackets are in very hard locations).
If you travel a lot or otherwise are moving around with it, get the 14.
16 was a bit big on airplane tray tables, but this one might be a bit smaller.
14: pro - lighter con - less screen for multiple windows
16 pro - multiple windows side by side, longer battery lift con - 5 pounds, won't fit in backpack