I think two is better than one.
Currently, I only have Jackson that is strictly my full responsibility and goes everywhere with me that he possibly can, but he's not really like an "only dog" because I still live at home and up until a few months ago when my mom's dog died, he always had her, and I visit over my dad's house usually 3 nights a week where they have two dogs. So, he's barely ever alone. Once I move out and get my own place, I 100% plan to get him a companion.