Itally trip Rome public transit

You've pretty much summed up your own answer. The Metro is usefull for those places or some outlying sites but not for central Rome or Trastevre. But the Termini area is convenient for access to the train station and/or airport. You pretty much have to taxi in/out on arrival/departure with your luggage. The other sites you mention are walkable from the center but those can be long (but beautiful) walks. For my money - I stay near Termini. Then I either walk to the central area or you can take buses since it is a long hike. But the walk there is downhill and back is a nice uphill stroll to walk off all the great dinner you had!

The bus system is more useful. We always stay in the Termini (4 times) area because of the convenience to transit. It is slightly on the edge of everything but the walking distances are not bad. Can walk to the Vatican in about an hour. And sometimes walking is faster because traffic can be a zoo.

I agree with Douglas. We stayed near the Colosseum and used the metro extensively and liked the area but it doesn't have the same charm as the Pantheon or Piazza Navona areas (of course, it doesn't have the same price tag either!). We used the metro to/from Termini for our arrival & departure. We also took it to the Spanish Steps for the Dolce Vita walk (in reverse), then walked back to the hotel from the Piazza Navona area. We also went to the Borghese via metro, but in retrospect I think a bus would have been a better choice. Our final full day in Rome, we took the metro to the Vatican, walked to Trastevere, and intended to take the bus from Trastevere back to our hotel, but mis-timed it and wound up taking a bus to the Piramide metro station and taking the metro from there. If you weren't staying near the Colosseum, that would be a good area to take the metro or a bus to. All in all, I would say the choice depends on your ability/inclination to walk vs. take public transportation, and whether you prefer a more attractive area vs. the convenience of easily-accessible transportation. While I think our base worked well for the type of trip we did, next time I visit Rome, I would probably elect to stay in the Trastevere or Pantheon areas.

Liz nailed it: It depends on your desire and ability to walk. We stayed near Piazza Navona in a reasonable-for-Rome apartment (130 euros) and walked a LOT, loving every step. It was 20 minutes on foot to the Colosseum, 25 to the Vatican. We did use the Metro to go to Piramide, out to Parco degli Acquedotti, bus to San Clemente, tram to Tastevere, etc., with our Roma Pass. If you are able to walk 6 or so miles per day, there is no better place to do it than in Rome. So much to discover as you move from sight to sight! Rick's walks are very good, and I also like the book "25 Great Walks in Rome" for walking tour ideas.

There is bus # 64 going to Vatican. Be very careful when using public transport in Rome. Nowhere I saw more pickpockets. Every time being on Metro or bus somebody tried, thank God unsuccessfully.

We stayed by the Colosseo and had the Roma Pass as well. The metro only has 2 lines. To get around, we used the metro, the bus, and did alot of walking as well. Rick gives a great tutorial on how to read the bus stop signs. The challenge with the busses is that they didn't have maps on the busses themselves that showed you where the bus stops are so we just tried to follow the route on our walking map to figure out when to get out. See if you can get a good bus map when you get there, maybe at Termini. I think Ron in Rome's website has a great section on how to use public transport also. Just be alert, wear a money belt for your precious stuff, and go for it. We were 2 females travelling and we felt very safe, didn't see any signs of pickpockets or anything, and believe me, we were looking because we had been so warned! We also felt very safe walking around late at night, there's a strong police presence, I noticed.