I always find Haydn more interesting than either. I think Mozart is largely overrated, with a tendency to use the same formulae repeatedly; I think popularity sustains his reputation on its own more than merit does. His music lacks the interesting polyphony and interaction between the parts that can be found in Haydn, and I think that this interaction makes Haydn's music considerably more attractive than Mozart's.
Beethoven is better, in my opinion, than Mozart, but his romantic leanings mean his work has a different appeal to me from Haydn's. Haydn, I think, is the most interesting figure of Classicism, but with Beethoven's music, while he shares many of Mozart's music's features (while sharing somewhat less, I think, with Haydn), the most interesting features are the features that he shares with the Romantic composers. However, I find that these features are underdemonstrated compared to later works, and Beethoven's Romanticism is clearly less strong than that of Tchaikovsky or Dvorak, and I therefore incline towards favouring those composers in preference to Beethoven.
