Personally, I didn't like Mewtwo's sprite in R/B, its lanky arms just didn't appeal to me. But I do think Nidorino had its best sprite in R/B. Although Nidoran (male) did have the eyes that most other Pokes had that just turned me off. Although Nidoking looked so fierce in R/B compared to Yellow. Rhydon had a similar pose in Yellow that just doesn't look menacing, but in R/B that sprite of him just walking up to you with the look on his face was really intimidating.