Problem with anti aspartame sites are, they come off as amature like most internet conspiracy theory sites with no credibility. THat and the fact that probably a large majority of the western world eats it on a daily basis, with MASSIVE numbers eating above the recommended limit, for decades now with no real issues.
When you look at the supposed symptoms for aspartame as with so many other supposedly bad chemicals, people list so many symptoms to such varying degree's it simply reads as hyperchondriac's(guessing spelling there, not sure i've ever writen/typed it before) listing all their systems and blaming it on whatever the current trend for people to hate is.
The funny thing is most of the symptoms are all known caffeine overuse/withdrawal symptoms yet they just get lumped in with aspartame. THe thing is most chemicals that DO cause issues normally cause a very select and repeatable problem, this is whats missing, massively widespread problems of which most are almost certainly caused by other things so it becomes a joke.
AS for caffeine not being good for a hangover, you're smoking crack mate, I've never taken caffeine and felt more tired, ever, its almost impossible as its a stimulant. Whats very possible is the sugar high from "normal" versions giving you a quick boost then the sugar low once insulin kicks in causing tired feeling, thats common and nowt to do with caffeine. Caffeine is damn great, best drug ever, love it and never plan to stop taking it. Fully addicted and I couldn't give a monkeys.
I drink diet coke, the sweetness of the silly amount of processed sugar in non diet drinks make my teeth feel horrible, its sticky, overly sweet and just nasty. Diet doesn't taste really sweet, its not sickening in large quantities, its not sticky so feels refreshing and doesn't cause sugar high followed by sugar low making you hungry or tired.