Unless you are under 5'6" and 90 lbs there are no good seats in Economy on the 788. It is configured for maximum revenue on very long haul flights with minimum comfort for the PAX. If you like staring at a a wall and don't mind having no storage for your things other than the overhead bin that changes slightly as you can select that "Preferred" experience by picking the first or second bulkhead. The exit rows further back on the left/right have more leg room, sure, but the tray table is in the seat so the seat is narrower and has hard sides on both the left and right...seems like a good idea when you pick it, but after 4 or 5 hrs gets a little tight if you are more than a petite human, and again, no storage other than the overheard bin.

On the MAX, the best seats IMHO are the second exit row as you get the extra leg room, the same seat width and the seats recline. Just be sure to use the bathroom in the lounge or the terminal before you board if your shoulders are more than 24" across as you will touch both sides of the mini lav which might be off-putting to some. If you can get the 2nd exit row and there is nobody in the middle seat it's actually a better experience than J (again IMHO) on that plane, especially with the COVID restricted service that AC continues to provide.