Ehhhh...
Doom can suffer villain sue status, but Harley is also undergoing Wolverine publicity as well. Doom has prescience and is older while Harley was a DCA character that got popular, but she's grown and developed a lot while Doom's just been... Doom... Hmmm...
I guess Harley just because, when she shows up, something interesting is likely to happen while Doom has to struggle with Fan4stic.
I am the gentle hand who heals, the happy smile who shields, and the foot that will kick your ***! - White Mage