My list would've looked differently if I had entered more titles of directors like Hawks, Walsh, Boetticher or Peckinpah, but i decided to limit myself to one title. Therefore there's no Wild Bunch, Red River or El Dorado. Only Ford and Mann have two because I like their work best.
I've considered doing the same thing Scherp but have decided not to for 2 reasons.
Our regular Top 20 has always been made on the basis that you should vote for your 20 favourites no matter what. So if you think all of Leone's are the best, vote that way.
If we just vote for one from each director the results become diluted and inaccurate. If you vote for Comanche Station and I vote for The Tall T and neither of votes for 7 Men from Now (just as an example) we have three great films under represented and something else gets a vote that it might not deserve.
So my list is heavy with Mann and Boetticher, but choosing one favourite over another is extremely tough. Especially the Boettichers as, after a while, one tends to blur into another in my memory. If I could vote for the Ranown cycle as one film I would.