I'd go with Rams personally. I have read many stories about Kribs who have killed their mates during the spawning process. Kribs are easier to Sex, which would make finding a definite pari easier, but I would recommend Rams over Kribs.
Overall, I think it depends on your setup though. Kribs will not spawn unless provided a cave-like structure. Rams will spawn on flat rocks or maybe anubias leaves. Think about it though. Sexing Rams is difficult and depends on the specimens, generally, females have more pink on their bellies than males, and the Male's dorsal fins are more pointed than the females.
I like Rams better than Kribs in my opinion, but it's all what you want. Rams are always colorful, active species, and like Kribs, they will readily breed with the right coniditons. Read up on both of the species.
www.thekrib.com is a great source for information on the two species! Good luck!