I don't use Rock types too often, but I do have my favorites:
Probopass has the greatest moustache of all the other Pokémon with moustaches and it has a rare type of evolution. It also has a great cry.
Cradily and Armaldo are by far my favorite ancient Pokémon. I've used both of them in R/S/E and they were extremely helpful against the Elite 4. I also like their designs.
Tyranitar has always been one of my favorite Gen. 2 Pokémon. It's powerful and it's also a pseudo-legendary.
Last but not least, Sudowoodo. It's watering can event in G/S/C/E/HG/SS makes it unique and Bonsly is definitely my favorite baby Pokémon. I thought it was so cool that you could use on in XD way back when.