I have toured solo, and I have toured with one or two friends. When my son was 14, we did a two day tour together, which I remember fondly. A highlight of my life!
Overall, I have no preference. I enjoy companionship when I am riding with others, but am content to keep company with myself.
If I were going cross country, my first choice would be to go with someone. But if nobody was available, I would not hesitate to plan it as a solo trip.