neither is sugar...they are artificial sweetners.
i personally think a little sugar, like in your morning coffee, is fine. when I reach for a sweetner that's not sugar, I use Splenda (aka sucralose), since it technically is a sucrose molecule with a chlorine atom bonded to it. your body can't break the bond, so the sucrose isn't broken into energy, and has no effect on insulin levels.
sweet n low is sacchrine I think...totally artificial, and high levels of sacchrine causes cancer in lab mice.
so again, fake sugar in moderation.