One of the most frequent questions I get from my own students and visitors is: "Where can I go dance Waltz, Foxtrot and have enough room to move." They want something different from the studio dance experience. What's in your city and do you have events worth traveling to? My students travel to dance. I would love to be able to suggest ideas.
The thread title is "... best places to dance Ballroom Socially ..." but the details in the post are much more specific: "... dance Waltz, Foxtrot and have room enough to move." Other people may have different criteria for "best".
For example, DH and I have recently decided that the Ballroom socials we have been attending for the last year may not meet our needs. They may be great for others, including your students, using your definintion. The socials are held in a large gymnasium; large meaning "bigger than two regulation basketball courts." They play a variety of music, including quickstep and VW in addition to waltz, foxtrot, cha cha, rumba, ECS, WCS, NC2S, salsa, etc. If you go with your own partner, that's great. I can even get a reasonable number of dances with other partners, if I make myself available or I ask the leaders.
But something is missing for us. The group is actually TOO large for our comfort (I don't estimate numbers well, but I'm sure it's usually well over 100). I came to recognize a few people, but I don't feel that we have joined a community. I admit that I could be doing more to reach out to other people, but I don't have to work as hard to make connections in my other dance communities. So we're looking around in our area for other options, and I've been considering the question of what makes a good social.
Looking at the physical aspects first ... how large is the space? What shape is it (taking into account odd corners, pillars, etc.)? Is there a single floor, or are there multiple rooms/spaces? Where is the seating for non-dancers or people who are sitting out? How comfortable is the seating? Where are the restrooms? Are they adequate for the number of people attending the social? Are there any other amenities such as snacks or drinks, and are they included in the price of the social or provided for a separate charge?
Looking at the social aspect ... how many people attend? Is the number a good fit for the space, so there is enough room to dance? What is the skill level of the majority of the attendees? What is the skill level of the best dancers? What is the skill level of the teachers (if there is a class before the social)? How friendly are the organizers? How outgoing are the other attendees? Do people dance primarily with the people they know, or do they reach out to strangers/visitors?
Looking at the music ... what is the mix of dances usually played? Do they play more "street" dances or more "Ballroom"? Does the DJ pace the music based on a pre-determined list, or does he/she respond to the energy in the room?
You also ask about events worth travelling to. This is also very subjective. Do you mean great teaching: exploration of great basic technique / styling / musicality / a variety of classes in one place (congress/workshops)? Great music: DJ or live band / street or ballroom?
So it might be helpful if the responses were to include information on at least the size (physical and usual number of attendees), mix of dance types, and, for lack of a better word, "friendliness" of the organizers/regulars to visitors.