Interesting question
Hard to answer though. There are different perspectives, some already mentioned.
First, what about the other weapons of mass destruction?
Well, I'd probably agree to andycapp, if you would have the chance to eliminate such weapons (and even if it's just the A, not B or C), you should take it. The mere existence of B and C doesn't imply a need for A, if you know what I mean.
Another thing is the indirect contribution to peace that nukes have had and maybe still have.
It was good that they (and other weapons of mass destruction) existed during the cold war, otherwise it probably wouldn't have stayed cold. Again I think, eliminating A wouldn't have changed so much, as B and C would still be there and should have been enough to prevent WW3. (Of course all that needs these weapon on both sides of a confrontation)
Now how about today? Eliminating nukes would still be "okay" in the sense of not threathening peace, as long as the other weapons would still remain on all relevant sides. It might be arguable if nuke are more effective in preventing all out war then B and C weapons but I'd think modern weapons of that kind would probably have the same effect.
But what if you could eliminate ALL weapons of mass destruction? Would that make war more likely to break out? I'd say yes.
Would it take away a hue threat also considering terrorism? I'd also say yes.
So what weighs more? It's a hard decision, but I would eliminate all weapons of mass destruction if possible. The threat would definetely be solved then, and war wouldn't definetely break out. That would be the decisive factor for me.