This is something that each person has to decide. There are some people who say that artificial sweeteners are tools of the devil
and some who say that there's no big deal.
I personally fall somewhere in the middle. In general I try to avoid processed foods as much as possible - and that includes artificial sweeteners. I do, however, drink Diet Coke once in a while (maybe 3x a week) and I don't think it's hurt my weight loss or that I'm going to die of some horrible form of cancer because I do.
I'd say do the research (from REPUTABLE sources, please - not scare sites) and make your own determination on what's best/healthiest for you.