I'm looking at flights from Denver to Italy in November, either Rome or Milan. Right now, flights are a bit cheaper into Milan than Rome. Is one city more preferable than another, as far as taking a train onto my destination, Firenze?
Check trenitalia.com for train schedules to Florence (Firenze Santa Maria Novella). Both airports have trains that run to the main train station (about every half hour). Milan's airport is further from the city center than Rome's. Both train stations have frequent trains to Florence.
Since you have to change planes from Denver to anywhere in Italy, also look at flights to Florence (FLR), Pisa (PSA), and Bologna (BLQ). All of these are closer to Florence than Milan or Rome.
From either Milan Malpensa and Rome Fiumicino airport, you would take a train from the airport to the main train station (Milano Centrale and Roma Termini, respectively; runs twice an hour most of the day in each case). You then take a separate train from that main station to Florence Santa Maria Novella (Florence's main station, often abbreviated Florence SMN). Trains from either Milan or Rome to Florence are frequent, and you should not buy this ticket in advance. Advance tickets are non-refundable, and you can't be sure of which train you will catch as you don't know how long the airport "formalities" will take.
DEN is a major United hub. United is partner with Lufthansa ( both Star alliance) and Lufthansa is the largest air carrier operating at Florence airport (both to Frankfurt and Munich). Swiss (also part of Lufthansa) flies from Zurich to FLR with 3 daily pairs.
See if you can find a flight DEN - FRA (or MUC or ZRH) - FLR with UA/LH/SW.
It might be a bit more expensive than flying to MXP but if your intended destination is actually Florence the extra airfare cost will be offset by the savings in time and train fare. The train fare from Malpensa to Florence (via Milano Centrale) is about €60 p.p. one way (€120 round trip). Plus when you return home from Milan, you need to spend one night at a hotel in Milan because flights to the US depart in the morning.
So even if flying to Florence costs you $250 more (which it won't), you are still better off flying directly to Florence (unless Milan is also in your intended itinerary).
Bologna is another option with plenty of Lufthansa and even British Airways options (via LHR). However in my 25+ year experience flying from SFO to Florence, I noticed that Bologna is rarely much cheaper than FLR and the one way train from Bologna to Florence is 25€ plus €6 for the shuttle from BLQ to the Bologna station. So unless flying to BLQ is at least $100 cheaper (never happened to me) I don't bother.
Check www.kayak.com:
From: DEN
To: FLR
If you want you can check multiple airport by separating destination airport codes by commas. For example in the destination box you put:
To: FLR, MXP, BLQ