Tours: How far in advance should I buy & better to buy now or in Italy?

Viator is a tour reseller, they don't conduct any tours. You'll need to find which company will actually be doing the tours and then find reviews on them before booking to ensure that you get a reputable tour guide. I would wait until your trip gets closer, say August or September. I like to tour on my own or with audio guides and find Rome a very easy city to explore. I've never felt the need for a guide to take us around the city. The only "sites" I would recommend using a guide for would be the Vatican museums and the forum. The forum is not well signed and a guide can really help you understand what you're seeing. The vatican museums are so large that a guide can help you see the highlights without being worn out. I like to tour with audio guides and a guide book. There are some really good ones out there if you like to tour that way. Donna

Thanks for your response and sorry for not clarifying, I was looking into viator.com to book tours I understand that they are not the ones giving the tours but are a re-seller. I have been doing a ton of research and reading reviews and it's a hard choice. I do however appreciate your feedback and will take your recommendations in consideration if and when i decide to book-might just do it myself like you suggested. Thanks

Sarah, One other option you might consider would be to book a private rather than a group tour, as that would allow you to tailor the sights more specifically to your interests. I would highly recommend Francesca Caruso (contact info in the Guidebook). She's an outstanding Guide! Happy travels!

I did also consider that, however it seemed to be more expensive to me then booking a tour through viator but I will e-mail her and see what she says. Thanks for the recommendation. By any chance do you remember how much she charged?