I think the 14” is more portable and less expensive, and the 16” has more screen, battery, and thermals.
I have been going back and forth with both today as I want to decide on one. Franky I would love them both if budget was not a question.
For me the battery life is not a huge point given they charge fast and can even use a battery bank if not near an outlet to top up the 14 in a pinch.
What I have noticed so far as differences not commonly mentioned :
1. Screen brightness. The 16 is a bout 1-2 ticks brighter. Depending on use case that could be handy
2. Typing experience. On the 2 I am using at moment I noticed the keys on 16 seem a bit less stiff. Also given the longer palmist the typing experience feels different. The sharp edge of the laptop hits my first on 14 and higher up on the 16. Can't say one is better but it might be worth testing if you plan to type much on them and are only use to 1 size.
3. Of course battery life and screen size are better on the 16 and portability on the 14 and thus one's use case might determine which you choose. For me as I stated battery less relevant as is overall weight, so it comes down to screen vs size.
The 16 inch is truly immersive especially lying in bed with it in your lap. Lying brain in an Imax theatre.
Despite the larger footprint it doesn't feel too bulky in the lap and the added weight makes it feel secure in place whereas the 14 feels it can slide around a bit more. For using around the house or minimal travel it is portable enough.
But man if I had to travel for work a lot or was a student taking my laptop to school each day? The 14 would be perfect.
As a dollar proposition regardless of anything else, assuming both devices are spec'ed same (for me 16gb 1tb 10/16 m1 pro), there is a difference of about 200$ US and then apple care is another 100$ or so different.
For the added cost you get:
1. Bigger screen
2. Bigger trackpad
3. Bigger battery
4. Bigger charger (140w vs 96)
Each of those is on the order of more than 30%
5. Bigger/Better speakers
6. Bigger fans and larger cooling system (quieter system with less heat buildup which bodes well for longevity).
So the 14.2 inch you sacrifice all of that to save 1.7x1.1 inch in area and 1.2lbs.