Best cities in Europe for a month long stay

My budget is $3,500/month. I’m in my mid 20s and enjoy museums, history, exploring cities, meeting new people, and hanging out by the water. I plan to spend each month in a different country to keep costs low and have a good homebase to work from and take weekend trips. I only speak English and would prefer places where that won’t be too big of a problem.

Given that, what do you think are the best cities to go with? I like the ones listed below but am open to any and all suggestions.

Schengen Area : Prague, Budapest, Lisbon, Canary Islands, Valencia, Porto, Ljubljana

Non-Schengen Area : Split, Dubrovnik, Kotor/Tivat, Sarajevo, Sofia

Best cities in Europe for a month long stay