90" from the floor means you'll have 36" uppers. That'll leave you about 6" to play with for crown molding. That's what you want. 30" uppers look outdated and cheaper. Plus you lose storage space.

93" with 3" of crown or 90" with 6" of crown so that there is no dust catching gap. What you DON'T want is 90" with 3" of crown.

Our standard practice is to use a 36" upper placed at 90" above the finished floor. Then we install a 4" plain vertical fascia on top of the upper. The crown moulding, which is usually 3-4" in height, is installed against this fascia and tight to the ceiling. This enables the crown mould to float on the face of the fascia, allowing adjustments for an inconsistent ceiling surface.

We chose to go with "outdated and cheaper" 30-inch uppers. Going 36" would not have added an additional shelf, so would have paid extra for no real gain in useable space. Wife struggles to reach top shelf as is. Instead, we purchased finished top and bottom panels for our uppers which provides a continuous flat surface to display items on top and covers the gap between uppers. Secondly we purchased galley rail to go atop all of our uppers. This continued an architectural detail in the adjacent dining area. The space above the uppers not only provides room to display items, it provides color and is less claustrophobic than running cabinets all the way to the ceiling. Instead of paying extra for hard to use upper storage, we chose all plywood construction, Blumotion full extension soft close drawer glides and got extra roll out trays for our twin pantries.