As you say, every one reacts to places differently. You won't know how you feel about a place until you see it. Remember you can't see everything on one trip, and if you only have 10 days, you will have to be brutally selective.
I highly recommend looking at Rick's videos about these places, to see what calls to you.
As for my own reactions:
I liked Luzern just fine, but it doesn't fit well with a short trip to Italy; save it for when you go to Switzerland.
Venice is unlike any other place, and I think it's worth seeing just for that - how a city has barely changed in hundreds of years. Yes, it's crowded, but it's also easy to get away from crowds.
Milan is a large, modern, fast-moving city. Many who visit Italy aren't looking for such a place, and don't like it. I like it a lot. In particular, the roof of the Duomo alone justifies the trip. It's also much easier to get around than other Italy cities (including many smaller ones), thanks to its efficient metro. If you're flying out of Milan, you'll most likely want to spend your last night there, and Rick's excellent Milan chapter will help you fill a day or two - even if it doesn't otherwise draw you.
Florence has the amazing Renaissance art, as well as great daytrips and beatiful views from Fiesole. I haven't been back in many years, but am planning to return later this year.
Lake Como is all about relaxing. It is lacking in "turnstile attractions" (Rick's great phrase), and is for seeing "how slow you can get your pulse." I also agree with his statement "If relaxation's not on your agenda, the lakes shouldn't be either." I should note that while I liked Varenna a lot, I wasn't taken with Bellagio at all.
I haven't been to the Cinque Terre.
Again, you can't go wrong with whatever you choose.