Likely the ones that are on the bandwagon early.

To be even more specific, in the early days now, the main allure of wasm is performance. So the focus will be on languages and toolchains capable of generating optimized native code. Out of those, look at which ones are easy for the developer to set up (both in general, and for wasm) on all popular developer OSes.

So, I'd say that Rust will probably be the biggest beneficiary.