They are not the same, 30p records each frame twice, if you shoot 30pN the duplicate frame is removed or you can remove these redundant frames when you capture the 30p into FCP. 60p has 60 frames, will be smoother and can be converted into 30i perfectly. The only reason to shot 30p is to save on HD space, IMO.
You can set the firestore to remove the duplicate frames and by doing so you get 2x the record time on the device. If you don't need the extra record time I would record 60p (59.94) If you need to down convert or upper convert to an interlaced format 60p works best.