Definitely subjective. I don't find some parts very readable. E.g., this line took my a minute to parse:

  append34 := func() func([]int) []int {

If I was going to rank the readability I would say:

1. Rust function bodies 2. Go code 3. Rust function signatures 4. C++ code

Which you could argue is me shifting the boundaries a bit, but sufficiently statically typed languages seem to develop two (or more) sublanguages. Global complexity definitely pushes Rust down peg.