its really your preference,
heres something i got from the atkins induction part of the web site

http://atkins.com/Archive/2001/12/15-464579.html
Artificial Sweeteners
You must determine which artificial sweeteners agree with you, but the following are allowed: sucralose (marketed as Splenda™), saccharin, cyclamate and acesulfame-K. Natural sweeteners ending in the suffix "-ose," such as maltose, fructose, etc., should be avoided. However, certain sugar alcohols, such as maltitol, do not affect blood sugar and are acceptable.

Saccharin has been extensively studied, and harmful effects were produced in the lab when fed to rats only in extremely high doses. The Food and Drug Administration (FDA) has removed saccharin from its list of carcinogens, basing its decision upon a thorough review of the medical literature and the National Institute of Science’s statement that there is "no clear association between saccharin and human cancer." It can be safely consumed in moderation, meaning no more than three packets a day. Saccharin is marketed as Sweet'n Low™.

We discourage the use of aspartame (marketed as NutraSweet® and Equal®) because of clinical observations that it slows weight loss in certain individuals. The FDA has approved the herb stevia for use only as a supplement, not as a sweetener.

The Atkins preference, however, is sucralose (Splenda™), the only sweetener made from sugar. Sucralose is safe, noncaloric and does not raise blood sugar. It has been used in Canada for years, and the FDA recently approved it after reviewing more than 100 studies conducted over the past 20 years. Note that each packet of sugar substitute contains about 1 gram of carbohydrate, so don’t forget to include the amount in your daily totals.