Visas for US citizens, for 6 month stay (Granada)

Hola, We are a family of four, planning to live in Spain for about 6 months next year Protected content . We don't plan to work and I'm wondering what is the best visa to apply for? I've looked at the consulate website already. Does anyone know whether they are selective about who they give them to? Or do we have a good chance of being granted visas as long as we do all the proper paperwork? Any advice would be a big help. Thank you!
UPDATE: Thanks for all the advice, I am so glad I asked. We applied for non-lucrative long-stay residency visas. Hopefully all goes well!