A lot of this is personal opinion...but my opinion would be to the bottoms of the hood, shelf and cabinets.

Otherwise I would do all the walls to the ceiling. Not sure where the doorways are for you to end the run.

I agree with Barnes - under the hood, shelf, and cabinets. If you do the whole wall, I think it can sometimes look weird if there's tile above cabinets.

Also, in the second picture, your island looks to be a light lavender color?? Are you going to play up that lovely shade in your backsplash?

Not actually an answer to the dilemma but I would remove all those upper cabinets they are not looking good as they are IMHO

Are you planning on doing crown to the ceiling on the upper cabinets?

A full crown to the top, no. But there is the possibility of a simple trim on top. thanks for the photos, that’s helpful. And no to eliminating the top cabinets. It‘s not designed for a magazine and might not be to everyone’s liking, but it’s a functional kitchen for us and we need the storage and quite frankly, we like it.

Go under all the cabinets and the lower shelf and to the bottom of the hood.. Normally I like the drama behind the hood but it looks like there was no space left on either side of the hood so running the tiles all the way won't look quite right there IMO

I like backsplash to be all the way to the ceiling. No break line of backsplash will make the space look bigger.

OP, what did you end up doing? Curious because I am close to the next phase :)

Any updates? Would love to see your finished kitchen.

Do you mind sharing the quartz you used and what did you decide with the backslash? Post a finish photo :)