Rhai is dynamically typed and uses reference counting, Rune has a full VM with a borrow checker, and Roto compiles to bytecode. The tradeoff is basically faster iteration with Rhai vs faster execution with Roto, with Rune sitting somewhere in the middle but feeling heavier.
khvzak has compiled some benchmarks. mlua and roto are some of the fastest: https://github.com/khvzak/script-bench-rs
Rhai is dynamically typed and uses reference counting, Rune has a full VM with a borrow checker, and Roto compiles to bytecode. The tradeoff is basically faster iteration with Rhai vs faster execution with Roto, with Rune sitting somewhere in the middle but feeling heavier.