I have mainly played in Solo, I switched to Open for that Planet Wilson incident and played that way for a while but as an inveterate CG player with mostly unmodified ships found that to fretful so I have decided to play in the Möbius group.
Play wherever you feel comfortable, and switch when you want to.
Quite a lot of the time when in Möbius or Open I have run into no more players than I did in Solo, mostly you find them at certain hotspots like Jaques, CG systems, Engineer systems and those systems (in)famous for their ability to boost your credit balance. Unfortunately the latter two have been associated with players more interested in ensuring that having gotten all the advantages these systems provide others shouldn't be allowed to do the same. But as I said most of the time you will see almost nobody.