You'll probably be fine either way, IMO - OCaml has a lot going for it, it's fast and incredibly quick to compile, and has a pretty straightforward execution model. Haskell is not quite the same (different evaluation strategy, different ways of organizing your programs), so there's a bit of associated overhead there, and for a beginner it can appear daunting.

The most important part of these languages is really how they try to enhance your abilities to write modular programs. You might be surprised to find out languages from the 1970s and 1980s have better abstractions (e.g. functors/modules) than some designed today. :)

But fundamentally I think some of it will come down to personal choice and aesthetics at some level; e.g. I really like Haskell's syntax (principled, block structured with no semicolons) and I really like laziness in general, because it makes it really easy to 'float out' and refactor code. OCaml has a much better module system, a very fast compiler, and is very well designed and thought out IMO. None of those are dealbreakers - it's just a matter of picking your poison.