Gnomes will win this one.
I'm OK with hobbos and monstrous races in general, but it is just an exceptionally awesome thing to turn invisible and stab something in the face when it didn't even know you were there.
I might be biased since I'm playing a gnome assassin ATM, but I think even if I wasn't, the hobs are not awesome enough.
Halflings suck in comparison to a gnome who knows how to play the archetype.