i personally don't like rock pokemons, they are weak against grass, water, ground and rock and it has strength against flying and rock (that i remember). i haven't used rock pokemons, so i can't tell you. what do you want a rock pokemon for, anyway?
I just one a pokemon of rock that can be much better than fire =D but i whant the best rock pokemon...
Tyranitar. Not exactly pure rock, but it does nicely. x4 weak to Fighting though... Aerodactyl Perfect lead. Watch out for Ice Beams/Fangs/Shards. Rampardos Sheer power, dies easily, slow. You need at least a fire move on your team to handle Scizor, Magnezone and other Steel types not named Heatran.
geodude is weak as hell, i guess you meant golem. onix is also very weak, but for me any rock pokemon is weak. if you want to battle fire then get a water pokemon. onix's evolution is stellix, it's a steel type, not rock
http://www.serebii.net/pokedex-dp/location/246.shtml#platinum or get a Flashfire pokemon to counter other fire types.
I dont have my M3 Here i am with N5 >I ... will if you have a tyranitar you can change it to me if you whant =D..... xDD
The only Rock type Pokemon that I really like is Golem, the others just look really odd for my tastes.
Rhyperior is the best, hands down. Solid Rock basically weakens Super Effective hits against it and it has an awesome defensive stat as it is. With Sandstorm, he comes a beastly Wall. Get yourself this and you'll be set... His 4x isn't even all that much to worry about, since Grass and Water aren't that used any more. Rhyperior Adamant Nature Leftovers - Stone Edge - Earthquake - Megahorn - Avalanche
man i used regirock in a battle but he was far tooo slow...! tyranitar is good... but i would go with rhyperior...