Duby has been absolutely great on Dalvik so far. Like I said, Duby is not a dynamic language, it just provides one of its main benefits through type inference and a drastically less verbose syntax. I translated the same code from Java to Duby (reducing its size and making it a whole lot more fun to work with) and noticed absolutely no drawbacks. That's not to say there weren't any speed decreases, but if there were they were too small for me or anyone to care about.

Do you have any benchmarks or references for Scala and Clojure's speed on Dalvik? I haven't been able to find much. (That's curiosity, not snootiness.)