There is no right or wrong answer, it depenRAB specifically on your body. Personally, I don't have any side effect at all from aspartame, but sugar is the single reason why my skin ever breaks out. You'll have to experiment on your own and find out how your body reacts to both substances.
Yes, most likely. Aspartame in general is bad for your health, it is in my opinion one of the worst artificial sweeteners out there. Stay away from all artificial sweeteners! There are healthy natural sugars that are recommended, like Stevia or Muscovado.