Stevia concentrate which is the sweetest components extracted ( via water process if you use the good stuff also available from Herb-Care)from a herb, or use the green more whole form or even the leaves if you prefer is much better than xylitol which is a Sugar alcohol.
Xylitol is DEADLY for dogs, as little as 3 grams can kill a 65 pound dog, much less for smaller dogs, even one or two pieces of Sugar free gum sweetened with xylitol could be enough.
I get so mad when I see all the gum stuck on streets and sidewalks that peole just spit out when they are finished...as if the eyesore wasn't enough the health risks to innocent dogs who are attracted to the gum smell are extreme.
Please read this article to see just how real the threat is: http://www.snopes.com/critters/crusader/xylitol.asp