IMO
11:
cheaper
light weight and portable.
Multi-tasking? Connect to monitor or TV or use laptop/desktop
Watching movies? monitor or TV is always better than any tablets
battery life is better than 12.9 m1 (I had both and returned 12.9)
12.9:
expensive
Heavy (much heavier with magic keyboard)
blooming (maybe?)
aspect ratio is not ideal for movies
miniled display is better for HDR content, no big difference to me for normal usage
maybe better drawing experience
I’d rather get a base model 14inch mbp tbh.
14inch mbp : m1pro, 512g, 16g for $1599 (on sale).
iPad Pro 12.9 m2 : 512g, 8g ram is 1400 , plus keyboard 350, plus screen protector, plus pencil, plus USB-C hub…
Just my own opinion
I have both the 11" and 12.9" M1 iPad Pro, both with Magic Keyboards.
I also have a 14" MBP (work laptop) and a 16" MBP.
I don't think the 14" MBP is a substitute for either size iPad Pro, especially since many people like the pencil. With the iPads, they are very mobile. Easy to toss in a bag or in the car seat because most people have a cover on their iPad. I have the cellular plan on my 12.9", so nothing beats the 'always on' use - a 14" MBP simply can't compete for connectivity.
The 11" is a little cramped to type on with the Magic Keyboard, while you definitely feel the weight of a 12.9" + Magic Keyboard.
Bottom line, if I only need to use the iPad for a little while, and might be moving it around the house with me, the 11" Pro is a winner. Especially used in bed, or if I need to do things while waiting in the car.
If I'm going to be using it for >30 minutes straight, the 12.9" is nicer with the bigger screen and full-sized keyboard.