Both have female main characters being sent off to an island because society doesn't like their kind. Cross Ange has slight yuri and ecchi while Valkyrie Drive has much more. Both are action anime.

Both shows feature a plot where girls are exiled to a prison island and left to fend for themselves. There's lots of violence in both shows (both of the regular kind and the sexual kind), but Cross Ange is much more bloody and gory, whereas Valkyrie Drive is pretty much softcore hentai