Vacation with friends or family members can get interesting. If every body pays their share it might work but there is always somebody that does not. My sister and I travel together a lot and we always make sure we are sharing the cost.
We've taken several vacations with friends and it has been a blast. Haven't done it in a few years but if we had the money we would certainly enjoy another one. We have lots of great memories and still laugh about things that have happened during several of our vacations.
I prefer traveling solo, with my husband or my husband and I with our kids. I do travel a lot with my Mom. I also don't mind when we have mine and my husbands parents join us as we do get along very well. Before I was married I traveled with friends, but stopped because there was always one girl who never had enough money and wouldn't say anything about it until we were already seated at a restaurant for example. She would pay her travel for the destination, but nothing else. And getting everyone together was really a hassle.