I've walked through the catacombs before, I've done a group tour and finally I took a private tour and let me tell you, the private tour is well worth the little bit of extra money that it costs. Trust me on this, especially if you think you may only do one catacombs tour in your life do this one.
Our Paris Catacombs guide, Victoria, was amazing. She helped us get from our hotel to the entrance and we did not have to wait in the long line. She was very knowledgeable and had many interesting stories and facts. Highly recommend spending the extra money for this private tour.