IMO, there are only two revolvers that are true must haves and both are variants of the same gun. Those are the model 19 in blued steel and the model 66 in stainless steel, both with 4 inch barrels. They represent the final evolution of the original M&P and IMO feature the best mix of Size, Accuracy, Weight, and Power for a Combat Revolver. In addition I don't think that it's possible to find a better handgun for training a new shooter than a K frame loaded with a moderate recoiling round.
BTW, at this point I don't own either, I was a bit late to the party. However, I do have a 4 inch model 67 that I purchased used and it's so well balanced that it's easy to shoot well with. Someday I plan on getting both a model 19 and model 66 when the budget and availability permits, however right now the 67 is a real sweet shooting wheelgun I will never sell.