Well, let's take a look at them.
Sp Attack: 55
Sp Defense: 55
Viable Physical Moves (One of each type)
Solid Rock: Great ability, keeps him alive longer
Reckless: Powers up recoil moves
The mighty Tyranitar!
Sp Attack: 95
Sp Defense: 100
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.
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. :)