Well, Tyranitar's threats are mainly:
Ferrothorn & Forretress (will wall you)
The main Pokemon you won't be able to hit super effectively are Heatran Infernape, but Stone Edge will be x1 (and STAB).
Infernape and Breloom usually have Mach Punch, and Scizor and Lucario have Bullet Punch.
Fire Punch will deal with the first 6 Pokemon on that list, while none of your moves will hit Keldeo or Infernape super effectively. If you go for Fire Punch, it means that Keldeo will resist all of your moves.
However, if you go for Earthquake, Breloom will resist all of your moves.
Having said that, I would go for Fire Punch. It will be able to deal with Ferrothorn and Forretress, the first will be able to use Power Whip and Leech Seed stall you, the second will be able to use Gyro Ball on you at least once (because of Sturdy), and what with DD boosting your speed and Steel being super effective, it will hit hard.
It also depends if you have counters on your team for Tyranitar's threats. Depending on the rest of your team, Earthquake might be more suited. If you have, e.g. Infernape or Darmanitan on your team, then go for Earthquake.