Artificial sweeteners scare me - to be honest!!! I know plenty of people use them. But, I don't like to. Splenda for instance tastes almost too sweet. That is my opinion anyway. I guess I would rather just have to real thing in there.
I also would prefer to use butter instead of margarine. It makes me uneasy to think about what is actually in margarine. My daughter has health issues already and I have a condition that could potentially be made worse by using things that are artificial. So, for those reasons I try to stay away from margarine and artificial sweeteners.
I think that the margarine melts and cooks differently than butter. And, maybe it is just me, but I think it tastes different. And, this could just be a show of my cooking/baking skills - but my cookies seem to turn our better if I use butter (meaning that I'm not skilled enough to compensate if I needed to!!! LOL). Hmmmmm!