For a pure physical sweeper that would be Attack and Speed. You can simply max out each. Tyranitar's speed isn't great but it would be good enough to OHKO a few pokemon.
Alternatively, you can accept Tyranitar will get hit and make him a "tank" by putting EVs into Def/SpDef/HP too. I would go for max Attack then split HP and Defense evenly. Maybe a little SpDef for security.
He's more likely to take physical attacks, particularly Fighting, although Lucario is pretty common and usually has Aura Sphere (special). Same goes for Mewtwo in Ubers. However, sandstorms increase the Special Defense of all Rock-type Pokemon so Tyranitar will get a boost from that.