i've been fairly happy with Leiningen but have no experience using mix - i'm curious to know what you really liked about mix that leinigen doesn't have.
$ time lein --help
...
lein --help 2,16s user 0,49s system 141% cpu 1,880 total
$ time mix help
...
mix help 0,51s user 0,51s system 129% cpu 0,789 total