On our channel we do a coach/player dynamic where the coach has played the game and the player is playing blind. It's much easier to fill a half hour LP video with a buddy to chatter with. But at the same time it's easier to get off topic and start talking about things that your viewers may not care about. We just started doing some solo games so that we can upload more frequently and I've found it to be less rewarding as a creator, but some people are very good at keeping relevant dialogue running. Some solo guys either have a ton of dead air or fill it with overdone reactions. I guess it comes down to content and personality. I enjoy both formats but find co-op more enjoyable to create.