I am gonna disagree for one reason, the Medicom Harley is based on an actual comic book version of Harley, the Jim Lee Hush version.
I am definitely going to buy both but the SSC one is not based on any real comic art or story. Sideshow took creative license with this figure and it has it's good points and not-so-good points but at the end of the day this not any specific Harley. This isn't Jim Lee or Terry Dodson or even Bruce Timm; not Hush, not Arkham Asylum or even Arkham City. This is Sideshow's interpretation of Harley Quinn, period. For that I give Medicom props because they made a figure based on an actual comic book.
To me, unless SSC bases the figure on a version of the character from an actual comic book the figure is just a generic Harley, no more, no less.