Python - lots of talk elsewhere about python. Great language for a beginner, but plenty of power there.
Ruby - a nice, very nice, OO language that fits me better than python does (but both are very good). I think in general it is less suitable for someone new to programming, and there isn't the same amount of teaching/introduction material as python
Sounds fancy. What about performance ARM-wise?
Python is (or can be) pretty damn quick. Ruby less so, although the 1.9 VM has made major improvements (there's still a lot to be gained, though). They're both extremely good languages for beginners.
My main gripe against Ruby is the conceptual difference between "underlying" types like int, float and so on and the "Objectified" versions - it's been done for performance reasons (although, looking at Ruby's performance, you wonder why) and breaks the orthogonality of the language. Python > 2.2 doesn't have this issue, and you can happily subclass, for example, "int" - for this reason I would probably suggest Python over Ruby.
 The default garbage collector is slow and non-bounded, object allocation is naive, and (with the 1.8 vm at least, I know it was being looked into for 1.9) code interpretation itself was hideously inefficient. Fixing these gets you an ~10-500x speedup depending on code profile (Yes, I've done all of these for the 1.8 MRI codebase, the fix to the last issue being suboptimal but workable, unfortunately contractual constraints mean I can't give them back to the community - I did try quite hard).