Hi, those are three of the greatest cities on earth. First off, Spring and Fall are the best seasons to visit. The Summer can be overwhelmingly hot.
In Rome, our favorite is Hotel d'Inghilterra: http://www.hotels.com/ho127046/hotel-d-i...&view=#maps
It is a block away from the Spanish Stems an within walking distance of many attractions.
In Florence, our first choice is Portrait Firenze : http://www.tripadvisor.com/Hotel_Review-...ce_Tuscany.html
Again, great location right on the river.
Finally, the spectacular Venice. We have had fabulous stays at two hotels, both on the Grand Canal: Bauer Hotel -
http://www.bauervenezia
And, Hotel Danieli
http://www.danielihotelvenice.com/?PS=LGEN_AA_DEMA_CBNG_TPRP.com/
And, Hotel Daniel -