Let's see, shall we?
Rhyperior
Pros:
- Very high Attack stat of 140
- An awesome defense of 130, covering its slowness
- Gets moves like Stone Edge, Earthquake and Megahorn all by Level up
- Rhyhorn is fairly easy to find
Cons
- Slow
- Very vulnerable to Grass Knot
- 2 4x Weakness, Water and Grass
- Low SpD, while most Water and Grass types are Special
- Rhyhorn comes a little later than Cranidos
Rampardos
Pros:
- A whopping Attack stat of 165
- Gets Rock Polish to tick off slowness
- Gets Earthquake and Stone Edge all by TMs
- Found earlier via Underground in Eterna City
- You can easily soft reset to get a good-natured one
Cons:
- Too reliant in set-ups (probably even needs a passed setup)
- Very slow
- Has like, nonexistent defenses
- Whether you get it or not depends on your TID, so its some kind of a gamble of time to get it
- Glass cannon
In this case, I recommend you Rhyperior.
Rhyperior @ Life Orb / Any
Ability: Lightning Rod / Solid Rock
Recommended Nature(s): Adamant / Jolly
- Stone Edge
- Earthquake
- Megahorn / Filler
- Thunder Punch / Ice Punch / Filler
Rhyperior is much more reliable rather than Rampardos because of reasons above. Though...the cost is a pathetic, double 4x weakness. Rampardos would've took this place if it is quicker, or at least have decent defenses. Sadly it doesn't
However...!
If you really want a Ground type, go for Garchomp. It's easily one of the best Mons' to grab in a Sinnoh playthrough. If you want a Rock type however, no worries - Garch gets Stone Edge
Garchomp @ Leftovers / Life Orb / Any
Ability: Sand Veil
Recommended Nature(s): Jolly / Adamant
- Dragon Claw
- Earthquake
- Swords Dance / Fire Fang
- Stone Edge
Rather than the two, Garch is much recommended. Garchomp hits just as hard and is much faster; an ideal fast physical sweeper. It tears through teams easily and is found just after Eterna. It also gets Fire Fang to cover the Ice-types which spooks this cutie a lot.
Hope this helps!