This list (which I run) checks whether listed servers are open or not. As for communities, they are not dependent on homeservers (minus the abusive ones), you can find rooms to join through https://matrixrooms.info and join them with your account on any reasonable homeserver. As for slowness, refer to the physical locations of each server; additionally see User Guide (in header) for a list of the most used servers. However, do keep in mind that resources and experience of each server differs.