If OP is a beginner, I think Elm's integrated approach (less fighting with build tools), pretty good docs, and larger ecosystem will be easier to learn than the more powerful, less united, and less documented ReasonML.
I've been doing a bit more elm (some at work) and I've tried to get into Reason from time. I always aborted on the first day. Last time I tried to learn ReactReason in december, I think their VSCode tooling wasn't working at all.