TLDR; On paper, Tyranitar’s Bite/Crunch moveset is the best. But in practice, you want to use the seemingly worst moveset Iron Tail / Stone Edge.
If you look at Tyranitar’s moves, the highest damage moveset seems to be Bite/Crunch.
Bite has DoT of 8.5, which is the same as Iron Tail.
Crunch as a DoT of 11.9 (9.5 + 2.4 stab). This is way higher than Stone Edge at 8.5 (6.8 + 1.7).
The weave DoT for Bite/Crunch works out to: 20.4
But this surface-level analysis leads to the wrong answer.
Bite / Stone Edge:
As KingKwongg astutely pointed out, Stone Edge is better than Crunch. Why?
Crunch locks you into a 3.2 second animation. And this happens three times per bar, for a crazy 9.6 seconds.
Stone Edge is a quick 2.3 seconds, and it’s only once per bar. This means, you can squeeze in a lot more Bites.
So, which is better? Crunch’s higher DPS? Or squeezing in more bites with Stone Edge?
If you run the numbers, Bite/Stone Edge comes out slightly ahead with 21.1, compared to Bite/Crunch’s 20.4.
So, Bite/Stone Edge is Tyranitar’s highest damage moveset.
But, highest damage doesn’t always mean the best.
Iron Tail / Stone Edge
Movesets have to be relevant to the current meta. So, Bite/Stone Edge is situationally useful against Dragonite and Gyarados. And Bite/Crunch is always the best against Espeon.
Defensively, you want to use Iron Tail / Stone Edge. This moveset does the worst damage 18.8 (11.9 + 5.5 + 1.4). And yet it’s the best.
The thing is, an attacker’s best move is to use Fighting mons like Machamp and Poliwrath against Tyranitar. Fighting does stacked super effective (1.56x). Also, Fighting resists Dark.
So as a defender, you want to avoid using Dark moves. If you look toward the bottom, Machamp’s advantage is reduced from 13.0 to 12.2. So, type advantage makes up for the DPS gap.
This leaves Iron Tail, Fire Blast, and Stone Edge.
Fire Blast (7.0) has slightly higher damage than Stone Edge 6.9 (5.5 + 1.4). But in practice, the Stone Edge is way harder to dodge than Fire Blast.
So there you have it. As a defender, you ideally want Iron Tail / Stone Edge.
If you’re using Tyranitar as a counter to Espeon, you want Bite/Crunch.
You could use Bite / Stone Edge against Dragonite and Gyarados. But this is situational against specific movesets. And, you really should be using Cloyster and Jolteon anyway. So Bite / Stone Edge really becomes just a high damage all-around attack moveset.