I like xylitol, made from hardwood, in my tea and coffee. It's not thatttt low calorie at about 10 cal per big spoonful, but I only use one. Honestly I try to sweeten things with fruit like yogurt and cottage cheese, put a tiny bit of stevia in it if it's really bland.
Have you thought about just using a sweetened but low cal creamer? There is also some really yummy sodelicious coconut creamer you can put in your coffee that is pretty low cal and sweetens it just enough.