Obviously there are going to be up and down sides for working solo, as well as working with a team. I personally prefer working solo, but I also have the experience of working with other people. Here's a summary of the up and down sides for both choices (from my personal experience):
Woking Solo:
- I can do whatever I want and go with whatever crazy ideas I have
- I can choose to have my own pace and therefore everything would be less stressful
- If I think something is not good enough (especially art-wise), I can simply go back and fix it myself without needing to worry that I'm going to hurt someone's feelings
- Down side would be extremely heavy workload
- And sometimes I don't realize the problems with my game because I'm too familiar with it. You would need to find people who are willing to play test your game and provide feedback
- It also highly demands you to be good at a lot of things, unless you're ready to spend a lot of money commissioning people (I've only work with 2D games so far so I'm mostly talking about making the art yourself. For 3D games I assume you can just buy assets online)
Working with a Team:
- More divided workload obviously
- Better quality if you find the right person to do the right thing
- Down side would be spending endless time discussing ideas with your team, and sometimes you might get people who think they know what they're talking about but they don't (I've had someone who's extremely aggressive and would get mad at anyone who disagrees with her, even though her ideas, in my opinion, was absolutely horrible)
- Sometimes it takes forever for one person to do their part, and you have to wait till they finish their job before you can do yours (Even worse, sometimes they end up just not doing it at all but at the same time are too embarassed to let you know that they don't want to do it anymore)
- Conflicts, conflicts, conflicts... (I've witnessed many group projects getting cancelled due to conflicts between team members)
As you can see, I personally had a horrible time working with a team, and that's why I enjoy working solo a lot more. But at the same time, that's just my personal experience and shouldn't be a representation of what working with a team is like as a whole. So my take is just, if you find the right people to work with, and are good at dealing with them, then working with a team could be a blast. But personally I'm not someone like that, so I'd rather work on everything myself.