Depends on what you're looking for regarding price and type of accommodation.
Check out www.venere.com
Very easy to choose hotels according to location on this site. Search by area by clicking on "Find hotels on the map". I'd stay somewhere central like Navona, Colosseo, Spanish Steps, Trevi or northern section of Roman Forum area. You can walk everywhere from these areas. They are the more expensive areas but very handy and have a wide range of accommodation on offer...
I have stayed in Hotel 47 and would recommend it highly. Contemporary, well located, boutique hotel with spacious rooms at moderate prices. Not a great bar though but we were out most of the time anyway so this was not an issue or us.
We are also going to a wedding in Rome in October - we booked a (small) apartment in the Cavour area - it doesn't look a great area compared to some, but we kind of know the area & there are a couple of nice places to eat & a couple of bars & as we are only there for a few days I don't want to spend the first 2 getting my bearings! I would get the train in to Termini & get the metro from there to where ever you are going you can buy an integrated ticket (I think)
Just to update you - the apartment was a complete disaster!! We just stayed the 1 night got our deposit back & booked a small hotel = which actually worked out cheaper per night than the apartment.
Had a great time at the wedding & for the few days after that though.