As for DYS, I never heard him say anything about that.
I saw the entire Once Upon a Time: Sergio leone documentary and not the cut version on the OUATIA DVD. Tarantino comments: " OUATITW I loved so much watching it on tv as a kid. It's like how to make a movie, well a sergio leone movie that is. " So to answer LA's question a while back Tarantino does like OUATITW. As for DYS, I never heard him say anything about that.
It's from a genre he obviously likes and a director in Leone he admires. Now, I have no tangible proof, but I bet he's seen Duck You Sucker at some point in his life.
What makes you say he doesn't like it, Firecracker? Just because he hasn't directly referenced it in one of his own movies, or something else?
IMO, that doesn't mean he isn't a fan of it. It just means he hasn't mentioned it in interviews.