I choose Land Before Time 3. I found Hyp and his two friends very unappealing, as was the overall animation quality. I don't know what it was, but the animation was extremely rough, even in comparison to the first and second movie. The songs were no better, but they were never a necessity anyway.
Land Before Time 11 isn't my cup of tea either, but only because of the concept alone. "Tinysauruses"? Running out of ideas now? On the 11th movie, I'm certain. Yeah, I'm sure it would be easier to think up ideas that would do the original movie justice if the producers just took a break and stopped making these sequels every year.
I don't understand the Land Before Time 10 hate. At least it was relevant to the original, but whatever.