I was kind of disappointed that they didn't use her in "Gods and Monsters"
Artemis tried very hard to fill Diana's sandals (HA!) but Arty was a little bit more...shall we say vicious...than Diana and her Amazonian power wasn’t tempered with Wonder Woman's compassion. She even got into it with Wonder Woman's protege, Donna Troy aka Wonder Girl.
Diana herself even donned a new costume and tried to help Artemis acclimate to her new role, because that is how Diana rolls.
Queen Hippolyta's vision finally came true and Artemis was killed in the line of duty. But you cant keep a good woman down and though Artemis died....she got better. Since then she has taken on the identities of Javelin, Requiem, Shim'Tar and Polemarch.
So which one is the best? Well Diana is the better Wonder Woman without a doubt. But technically Artemis is a better fighter (which is saying something), because as Arty herself put it, Diana relies too much on the powers the Gods granted her.