What is the best erectile dysfunction drug to take?

Depends. It'd be nice to know the cause. Some men lack testosterone, whereas others have problems with penis vasculature or nerves that are not working properly. Viagra, Cialis or Levitra (vardenafil) are frequently used empirically, meaning without knowing the cause for sure and all 3 of those appear to be equally effective between themselves.
Erection Medications. They are all equally effective. It is a personal preference.