We typically do a stacked molding to get to the ceiling height.

Go for the 42"cabinets . They will look fine once everything is finished and you will love the extra space for rarely used items such as a turkey platter or extra glasses.

No gap between cabinet and ceiling with 8' ceilings! We did 36" uppers with stacked crown just like you have, it looks great. Second kitchen I did this way, I'm surprised they are both telling you not to do that.

Get 39” cabinets. Room for crown and more storage. 42” has no room for crown with 96” ceilings.

I do not see how your KD will fit "42" cabs up and put a crown on them to finish to ceiling height" with your 8' ceiling. The math is wrong somewhere! Ask your KD for more detail. Your ceilings are 96". There should be 36" from floor to counters, plus 18" from counters to bottom of upper cabinets. Subtract 36" and 18" from 96", which leaves 42", and no room for crown at all. I suggest 39" tall cabinets with 3" crown. That will fit.

I am not a fan of the filler. It provides no utility and is expensive, so I prefer just 3" of crown, that's it. I'd rather have more storage - more air space for each shelf in the cabinets. Many cabinet companies make 39" tall cabinets. Maybe not the one that your KD is using (evidently). These days 39" cabinets are common. I'd tell your KD to use 39" tall cabinets, or find another KD.

You mentioned that the cabinets might look narrow. Perhaps post your kitchen design on this forum; maybe you do have too many narrow cabinets. The 15" cabinets you mentioned is pretty narrow. I hope your base cabinets are mostly drawers - are they?

We have a small l-shapes kitchen and yes we have 2 drawer sets a lazy susan corner cab and one butt door cab plus stove and dw for all base cabs . Also an awkward window/sink layout which leads to some narrow doors. As you said I have had 3 different design inputs on cabs, all 3 said 42" uppers and a crown. I couldn't fidure out how the math worked on that, but yielded to the pros. makes me think they were saying 42"and quoting 39! Thanks for the input

To clarify a bit I was getting way different advise from two of the cab installers, one said he makes fridge opening 37" so plenty of room to install fridge. other one just 36" so it slides in tight and looks built, just one example of several different design options. We had a design done today we could look at, with the filler up to crown and we like it so will go with that. Thanks All for opinions