Well, let's take a look at them.
Rhyperior
Stats
HP: 115
Attack: 140
Defense: 130
Sp Attack: 55
Sp Defense: 55
Speed: 40
Viable Physical Moves (One of each type)
Rock Wrecker
Earthquake
Megahorn
Superpower/Hammer Arm
Return
Poison Jab
Crunch
Aqua Tail
Fire Punch
Ice Punch
Thunder Punch
Iron Head
Outrage
Shadow Claw
Viable Abilities
Solid Rock: Great ability, keeps him alive longer
Reckless: Powers up recoil moves
The mighty Tyranitar!
Stats
HP: 100
Attack: 134
Defense: 110
Sp Attack: 95
Sp Defense: 100
Speed: 61
Viable Moves
Well, I'm lazy, so I won't list them. Tyranitar's movepool is slightly larger, just by 1 or 2 more moves I think, so it wins, because it can use special moves.
Abilities
Sand Stream: Causes a sandstorm and gets an awesome special defense boost.
So I would go for... Tyranitar! It has more balanced all around stats, and resists Dark type moves for your team. Even though the rest of your team will be hurt by Sandstorm, it isn't really that big of a deal and lefties can fix that. Plus, T-Tar gets that special defense boost, making it a monster to take down.
I may have overdid it, but I had some time to kill, and what better to do than list the stats, moves and abilities of them. :P Hope I helped you make a decision. :)