I would have to say Bichon Frise. My son has severe allergies along with Cystic Fibrosis so we had to find a "hypoallergenic" dog. My kids named him "Haku" and he has turned out to be a wonderful and invaluable companion to my son. Not only is he sweet natured, playful, and able to do all kinds of cool stunts, but he alerted us to when my son was acutely ill.
My son Malachy actually had a life-threatening seizure due to high blood pressure when he was 16. Amazingly, whenever his blood pressure was dangerously high after that, Haku refused to leave him, whining and even growling, which we quickly learned was his way of alerting us. Many times when EMTs arrived to tend to Malachy, Haku was protective until Malachy told him it was okay.
Bichons are smart and loyal and our little Haku has literally been a lifesaver!