I think ideally, no sweeteners of any kind.
If weaning off sugar is a deal-breaker or a favorite treat-recipe requires a sweetener, then stevia seems to be the preferred artificial option and honey/maple syrup the best natural ones. All used sparingly.
I've hardly sweetened anything since I started this. I've made the chocolate baked custard from the PB cookbook and added maple syrup to that. I get small amounts of sugar from very dark chocolate.
Zone diet on and off for several years....worked, but too much focus on exact meal composition
Primal since July 2010...skinniest I've ever been and the least stressed about food