lojban.
in all seriousness, i think that arabic would serve a little better, just because it would seem that there's a larger amount of business conducted in the world in the arabic realm; i'm not entirely sure which would be better though. arabic has some interesting semantic rules to it! both involve learning a new alphabet; the cyrillic alphabet is a lot easier to get down than the arabic abjad though. i guess it really boils down to which you feel might suit your purposes more; do you plan to interact with more people who know russian, or more people who know arabic? you shouldn't learn a language unless a.) you're addicted to learning (like myself), in which case, i say learn both, or, b.) you have an actual purpose to. it may not be the most serious purpose in the world, but that doesn't change the fact that there's a reason. these are only my thoughts though. ymmv.