both are so far away from being abused in the manner your speaking that it's hard to rationally comment on your concerns, gf. AI in particular. nanotech is a truly awesome technology that already HAS many very productive uses. but if you're talking about self-reproducing, semi-intelligent robots . . . not much of a concern. it has loads of potential in the medicinal sciences.
like ANY technology, either could potentially be used for ill OR good. but that's been the case ever since man first invented a sharpened stone to cut with . . .