I personally found the syntax in the ML series languages to be clearer when learning. I found Standard ML/NJ to be even easier (and potentially nicer) than OCaml for what it's worth.

I think it comes down to visual cues. Haskell eschews syntactic sugar and I personally find it hard to read the structure of expression. I found ML to be more explicit.

That and the community around Haskell really loves... clever... constructions. And its type system is more expressive but also complex from a mental model POV.