DEMI had (has) some replay value, the ballads are especially strong, while the up-tempos are a little weak but still cute for what they are. Overall a little forgettable but not bad at all.
Stars Dance is fun but almost mind-numbingly sugary, repetitive and overproduced. It lacks any artistry or personality (not only in Selena's voice) besides "I'm really horny" and "I wanna party" which is probably why ATRL prefers it.
Neither are particularly strong efforts but I prefer DEMI.