As I've said before you can get Diet Coke with Splenda. That's what I get. It taste like RC Cola if anyone remembers that stuff.
Yeah that is definitely a better route. The problem is it's hard to find at some vending machines around here so drinking aspartame based diet sodas once and awhile won't kill you, but just keep it under control. But like Vortit said, Splenda based sodas are a much better option.