Can't tell you which is the best as such but I initially tried things with aspartame. I didn't link various muscle pains and cramps to it straight away. It was only when I stumbled upon something on the web that I decided to try sucralose. All the pains faded away soon after.
Some people don't seem to get on with any sweeteners and have a total intolerance.
Stevia is a natural plant extract and seems to be ok to me at least.
I don't know which is the healthiest. And I think 'best' depends on your palate. I have tried Candarel, Truvia, Sweet 'N Low, and Splenda, and have got used to all of them. I have a 1kg pouch of Xylitol which I haven't used yet. I don't have a dog or visiting dogs. I have found that I don't miss sugar at all now.