The nuclear scan uses a dye and the areas of the heart that are not getting an adequate supply of oxygen do not light up so I would say the nuclear would be the best test and least invasive way of testing to see whether the heart is getting it's oxygen supply. Unfortunately even that test can miss blockages. It did so in my case. The next route would be cardiac cath and they could actually see whether the arteries are clear and that the heart is getting a good oxygen supply. One thing that test will not show is smaller blockages in the capillaries and veins that they cannot see on an angiogram so I guess there really is no perfect test.
I have answered your question as a lay person not a doctor so actually saying that I know the answer for sure would be impossible, but I feel comfortable saying that those tests would be the best.