Since you're making it an either/or. It would be better for Iran to be nuclear armed. Pakistan, China and North Korea are nuclear armed, so what?
The alternative is that we end up involved in yet ANOTHER Endless Quagmire War. Really, how many times do you think we can pay for 3x the ADJUSTED cost of WORLD WAR TWO?, not to even mention how many more dead and disabled can we deal with?
In any case, it's a false dichotomy. Iran is not close to getting a bomb and even if it were there are other ways to stop it rather than attacking. Indeed, attacking will probably guarantee they will get a bomb, and sooner than they would have otherwise.