I have two chasing worlds: Plains/hurricane chasing and local chasing. Each have totally different characteristics in about every chase-related subject we discuss, including this one.
Locally, I have never chased with anyone. In 11 years, all of my WV/PA/OH/KY chases have been solo. There are a few chasers in this region scattered about, but none close enough to really team up on a chase.
In the Plains (and on other long-haul trips like hurricanes or east coast outbreaks), I am almost always with at least one person. In fact, it was other chasers (Dave Crowley, Bill Coyle, etc) who got me out of WV into the Plains. Since I started Plains chasing with a team, I'm rarely by myself during chase vacations.
If scheduling and distances prohibit me from meeting up with my usual chase friends, I'll chase alone - which happens from time to time. But, if I happen to meet people at a chaser convergence that are willing to team up, I'm always happy to have the company.
In all cases, I prefer to chase with a group/team. The weather by itself is awesome, but people make the experience more enjoyable. Also, more people means more brains and more non-driving hands/eyes - which often means better decision making, navigating and spotting of features.