I would not put any artificial sweetners in my food. That has been too much written about aspartame, splenda and the rest. Splends's claim to fame is that it is made from sugar. So it has to be OK - right? The process of making splenda converts the sugar molecule by bonding chlorine atoms to it. A man made process.
I use stevis packets for tea and other drinks. I have found no after taste. Perhaps you are using too much. Stevis is a natural product, not artificial.
Try different brands of Stevia. For some reasons, one may taste bitter to you but another might not (someone suggested it to me and I found one that is okay).
I would feel safe eating Splenda. It is being used much more often in foods now and some companies that used to use Nutrasweet, etc.. are switching to it. To my knowledge there have been no studies showing it to be unsafe. Don't eat too many foods with artificial sweeteners though b/c it may give you a runny tummy.
Although you are on the Atkins Diet....please eat some fruits and veggies b/c they are good for you!!!!!!!!!!!!!!!!