The ClubSport DD+ has more torque (15 Nm versus 12), the Fanatec QR2 ecosystem and a higher rubric score; the La Prima is the cheaper base with Asetek's industrial build. So you are weighing a stronger, better-connected Fanatec against a cheaper Asetek entry.
If you want the extra torque and the Fanatec rim catalogue, the ClubSport DD+ is worth the step up. If Asetek's build and a lower price matter more, the La Prima is the pick - it just gives up torque, ecosystem and score to get there.