(admin: merged from another thread) 
I voted for other, as it is the Back to the future trilogy, that is best imo. It wasn't conceived as atrilogy initially, but expanded after the success of the first, but I think it makes a perfect whole, with the second part being the best. 
I love those three films, because they seem as one long film to me. 
As for the excuse, why I've voted for a trilogy that wasn't planned as such, The Apu trilogy was also completed with the second film, and the third was kind of added afterwards. :)