I don't know where you come from, but you're in for a huge treat!
Choosing an ISP in Italy is like playing Dark Souls with your character barehanded and your controller unplugged.
First thing first: forget about getting the speeds they advertise. They're - of course - the max speeds allowed by your connection, but the variables involved are usually all against the customer.
Even in big cities, switches are too few to handle the amount of people with a connection. So, even if you're lucky and you're apartment is right near a switch (also: there is no way to know it because: 1) there is no data available to examine; 2) your ISP could connect to a farther switch because reasons - and I'm one of these cases...), your speed could be just twarthed by the simple fact that too many connections are plugged to that same switch.
Also, forget about upload speed. 0.5 Kbps are the norm here, even for business plans.
BUT if you can get your hands on a fiber connection - and Rome is more or less 50% covered - you should be fine, even more because they cost the same as non-fiber.
I know for a fact that Fastweb fiber (here you can check if your address is covered:
http://www.fastweb.it/AVT/ ) is really good, but I don't know anything about Vodafone and Telecom.
As per the fact that I'm on a Fastweb non-fiber at home (coverage stops at the building right next to mine, yay) and Telecom non-fiber at office, I can say that:
FASTWEB (at home)
1) promised 20Mbps, got 5Mbps top, because I live in a recently built overcrowded neighborhood served by a single old and far away switch (there is another one nearer, but the customer care doesn't give a fuck), and the connection decays too much before getting to my place;
2) my router (Fastweb gift, as until some years ago Fastweb forced to use their routers) is old and shitty, but they don't want to change it if it isn't broke, so hey, for me Fastweb sucks A LOT, but at least not as much as...
TELECOM (at work, so this is a business plan!)
1) overpriced shit, and I mean literally: they sent us bills with like 3x the price we had to pay, and we had to involve a lawyer to solve that shit;
2) promised 20Mbps, got 10Mbps, even though the office is like around the corner from our switch, in an undercrowded (is this a word?) area;
3) it has an erratic behaviour, like once a month our work day starts with a call to their customer service because we aren't online, they say "hey you're right!!! we're gonna fix it asap, our tech people will send you a text when they're going to start fixing your line!", then we wait 2 or 3 hours, the line is magically fixed and a couple of hours later we get their text telling us they're going to fix our line in the 24/48 hours.
So... yeah.
The best advice I could give you is: ditch the super-low-cost crappy ones (like, Tiscali, Tele2, and I don't know nowadays whichever else), and stay with the big ones (Fastweb, Telecom, Vodafone), because they sucks hard, but not as much as the crappy ones.
