I feel that City Passes are almost never worthwhile! They cost a lot of money and you have to visit a large number of places in a day or two to justify the cost. If you are like me, you don’t want to have someone dictate what you must see and when. Visiting Italy is not about how many places you can see in a day but about the experiences of seeing places, meeting people and tasting the wonderful food & wine.
Skip-the-line Tickets are worthwhile for sites with very long lines. The major attractions can have lines of 3-4 hours long. I for one do not want to spend my vacation & visit to Italy waiting in lines. Skip-the-line tickets allow you to show up at a time and jump to the beginning of the line. They do cost more than the attractions cost of entry but you save the line time.
This YouTube video explains all about these two types of tickets.