Stevia made me quite sick so start carefully if you choose to try that.
For weight loss, the best sweetener is basically no sweetener. A low-GI fruit like grapefruit or lemon is about it. If you're really off sugar, properly brewed water kefir tastes surprisingly sweet even though all the glucose and most of the fructose is gone--but to people who use sweeteners it tastes like vinegar. I know because I thought mine was delicious but all my SAD taste-testers made horrible faces. :O
Don't lose all hope, though. I've found that second best is unprocessed honey. If I don't average more than a tablespoon divided between 2-3 mugs of coffee, my BG is level and weight loss is nice and steady. I don't use a scale but I use a tape on my waist and watch the fit of my clothes very closely.
Otherwise, I strictly avoid sweeteners and I limit sweet fruits to tiny portions no more than twice per week. I'm hoping the sweet fruits can be eaten more often when I shift to maintenance.