Milan or Genoa? (as part of a longer trip) - please advise :-)

Milan is more interesting, but bigger, but more convenient to get to.
You could see The Last Supper (reservations required).
Think you have to do your research and then make your choices. Only so much we can say, it's a matter of preference and judgment.

I think you would enjoy Milan more.

I’m not a fan of either city. Personally I’d head to Turin. Great sites especially the Mole Antonelliana, Madama Palace, Egyptian Museum, National Cinema Museum and the National automobile museum among others.

In December, we spent 5 or 6 nights in Genoa, and over the years have spent maybe 8 nights total in Milan. I read your description of what you like to do very carefully, and it seems like my husband and I like and don't like many of the same things you do except that we love the good, local, non-fancy food in all the different regions and towns of Italy and we tend to prefer medieval architecture over any later period. So, here's my take on your question.

I would return to Genoa tomorrow just to eat the food there again, but we have looked and looked for the kind of places we like to eat at in Milan and only found one. Plenty of sushi etc and fancy food and non-local food in Milan --- it's a big international city --- but it doesn't seem to have neighborhoods full of great places to eat like Rome does.

Genoa has the kind of historical district that I think you would enjoy --- it's mostly within what used to be the old city walls with lots of pedestrian-only streets. Milan has great things to see, and you listed every one that we have been to and enjoyed, plus there are more. But it's a big city and these places are in pockets dotted all over and it is not all that enjoyable or quick to travel from one to another (although the old-fashioned trams are fun). I do not like city traffic or walking on busy city sidewalks, so for me, Milan is not "walkable" even though technically you can walk there --- in the old center of Genoa, you can just wander.

However, when it comes to the cemeteries, Milan wins hands down. We have been to the famous large cemeteries in New Orleans, Paris, and Rome, and we even took a day-trip back to Genoa after we had already moved on to another town just to see the cemetery there. If you like extreme, melodramatic, over-the-top, gigantic, horrifically sentimental, idiosyncratic cemetery sculptures and monuments, then Milan's monumental cemetery is the place to go. Easily beats any other we've seen. Plus it is super easy to get there, whereas Genoa's means a bus ride or taxi. Genoa's cemetery sculptures are far less flamboyant and fewer, and the main thing we liked about it (besides a few individual statues which were wonderful) was that all the sculptures were covered in a really thick layer of dust, as if they'd been snowed on except it was dark gray --- we thought that was cool.

It is a snap to travel by train from Milan airport to Genoa --- we did it after a long flight from Minnesota with a 5-hour layover at JFK. We've done the same thing Milan to Venice by train --- also easy and quick.

Torino, since someone mentioned it and we were just there for 6 nights, is far more walkable than Milan and has neat little neighborhoods with good restaurants and some great art and the kind of architecture you like and the fabulous Egyptian museum. I have no interest in cars whatsoever and LOVED the car museum --- it was a huge surprise.

Probably obvious to say, but Genoa will not be anywhere near as heavily touristed as Milan --- I don't recall even seeing a non-Italian tourist in Genoa.

I'm glad to see someone else who loves cemeteries so much! In both cities they look amazing. I'm tempted to stay in Milan just one night to see Milan's and move on to Genoa for everything else you mention.