The way I see it, Saudi Arabia might oppress its own people slightly more than Iran does (Iran only deserves a little credit for its quasi-democratic institutions), but it's also much less of a threat to international peace. Yeah, Saudi Arabia does throw its weight around in the gulf (see e.g. Bahrain), and individual Saudi Arabians fund awful causes, but state policy doesn't support anything nearly as harmful as a WMD program or the "annihilation of Israel."
I guess if "being allied with Iran" meant that Iran stopped supporting terrorism and regimes like Assad's, I might consider that option. But Saudi Arabia would still have the advantage as a more important producer of oil, and as a more natural ally of other Sunni states such as Egypt.
Stop regurgitating State Department talking points. Saudi Arabia (and let's be honest, the United States and Israel, not to mention Qatar/the UAE/etc.) are far more culpable in state terror than Iran (whose supposed nuclear weapons program is a clear reaction to American and Gulf Arab aggression against it). If we're going to stop Iran from having a nuke, why should the genocidal apartheid Zionist state have an arsenal of over 200? For that matter, why should the United States, by far the worst aggressor of any nation since World War II, have nuclear weapons?