best route

It depends on your flight options. You can just do a day in Milan if you have little interest and there is a great direct flight. Check all of the options.

Milan has the "Last Supper" painting and the Galleria, it would be worth a day. If you want to relax then take the train from Milan to Varenna, on lake Como and spend 2-3 days just riding the ferry to different sights on the lake.

The other trip would be to fly to Venice, then the train to Florence , then the train to Rome, this would be very easy and you would seen the best of Italy in 10 days with minimal time traveling between cities.

I think Milan is often underrated for some reason. It has some great sites. We have always enjoyed our visits to Milan. It is worth a couple days at least if not more.

If you only have 10 days, including the days you arrive (half day lost just travelling) and leave ( most of the day lost just travelling), then I don't think you have time for Milan. I'd scrap it unless the flight home from Milan was greatly cheaper than from Rome. It makes geographic sense to go Venice to Florence to Rome to home.

As stated above, Milan has some great sites and is underrated. Depending on your transportation options/costs it's definitely worth at least an afternoon/night! On our first trip we did what you're contemplating - flew into Rome, took the train to Florence, then Venice, then Milan and flew home. I would do Rome for 3 days, Florence for 3, Venice for 2, and Milan for 2. If your 10 days includes Prague, then I would do 2 in Prague, 3 in Rome, 2 in Florence, 2 in Venice, and 1 in Milan.

Decide what city you’re going to fly home from and then decide on where to go.