Verona or Lake Garda

I would stay in Verona. We took the train to Lake Garda (Desenzano) as a day trip from Verona, and I wish we had spent another day in Verona instead. In late April, the ferries on Lake Garda weren't running on their full schedule. It was a pretty train ride though. Check the ferry schedules before you commit to spending time on Lake Garda.

I would spend the night in Milan and head to Florence from there, instead of backtracking to Verona.

We enjoyed Lake Garda. Look at Salò, popular with Europeans, not many from U.S. Lovely waterfront town with a promenade along the shore.

Verona will probably be the best to use as a hub. You stated you were planning 2 nights in Venice. You might consider spending another night there. Your first day there you'll probably be jet lagged and tired. That only leaves one full day when you will be back to normal. Just something to consider.

We loved Lake Garda this September and spent a week in Bardolino which is very popular with the Europeans. Prices were great and the food, wine and Gelatos were delicious. Seemed like everyone was there to relax, eat and have fun. We took the ferry ride to Sirmione which is very touristy but once we go through the hub it was great to explore the ruins at the tip of the island where some beaches are located. We had previously visited it on a day trip from Verona. Lake Garda would not be an easy hub like Verona where there is more to see although we did get on the once a day train straight to Florence from there. We pass through Milan in one day as our planes land there.

I think either would be fine. We stayed in Desenzano which we picked because our group wanted to stay on the lake but we could have easily picked Verona. Not sure I would visit Milan with such short time allotted to this part of the trip. I would add one night to Venice then 3 nights in either Verona or Lake Garda then head to Florence from there.