How many people are in a VA or VO?
Some VA’s have more than others. For example BAVA have 200+.
VA/VOs are not allowed to really advertise on the general categories. To prevent this from turning into an advertisement thread I will say that there is a very large number of users who are part of an organization.
Each organization has different elements that attract pilots. Routes, size, advancement, etc. If you are interested, check out ifvarb.com to browse the list of active ones to do your research.
Hope this helps and thank you for understanding.