Assuming the same implementation effort & skill: WASM, hands down (disclaimer: I have significant RISC-V experience and am an stout advocate, but RISC-V is a poor replacement for WASM).

ADD: a few of the reasons:

- When JITing RISC-V you cannot tell which are the last use of registers without a very expensive whole-graph analysis. Without that, you will have to generate more code than necessary.

- WASM's representation is very close to what you want in the compiler. In particular, you can directly tell all incoming control-flow edges, which makes analysis much more precise, gives optimization opportunities you would otherwise miss. Recreating this information from a binary is either impossible (due to computed branches) or expensive both in terms of analysis and the guards you have to generate to protect your assumptions.