Dark or rock tyranitar?

I would choose SD - it's limited and if you have second thoughts, he can always be changed .

(Honestly though, I haven't used my rock team since the birds went away, but use my strongest dark team regularly to provide bulk after Gengars.)

Both have different effectiveness profiles, and in a vacume, the difference between both sets is actually quite small, with neither double dark or double rock being better (infact the best set for tyrantiar when both rock and dark are euqal in effectiveness Bite/Stone edge)

Over all, Rock tyrantiar has little competition but its legendary match ups, which is how I personally measure pokemon is quite small until generation 5 now that the birds have come and gone recently. Meanwhile Double dark has a lot of match ups in the near and far future with the lake trio, presently cresselia and deoxys, but it has competition from legacy mewtwo and gengar, currently released weavile and eventually shadow ball darkrai who actually eclipses mewtwo agaisnt anything ghost's super effective against that psychic isnt as well in addition to resisting those types better, but tyranitar outlasts all competition while still maintaining very high DPS. It future match ups, while a bit of a ways away are still legendaries, the entire gen 7 trio, and for lower raids, there have frequently been tier 3's it destroys well.It seems to be One set is the best at what it is, but doesnt see as much usage, while the other isnt the number 1 best pick, but it has many consistent match ups for the rest of the series

There really is no general 'better' or more useful set when looking at these 2 pokemon on their own, what really determines it is what you have already for ghost and dark types. if that's what you lack, i'd say double dark, but if you're set there, go Smack down.

Make it a Rock Attacker because it's much more exclusive. You can raid Tyranitars, likely after this event is over they will re-release it because its a legit counter vs Cresselia, and they can always be made as Dark attackers, but Rock ones are only this time and now.

I would suggest getting SD next weekend. But NOT powering up the Tyranitar just yet; you've got 4, you likely don't need any more right now. But if you evolve it during the special CD, you will have the option to change it to a Dark attacker in the future - and you can't change a Dark attacker into a Rock attacker with TM's.

Once we know how Rampardos is going to be implemented in the game - and whether its actually going to be a useful Pokémon or not (Hi Deoxys...) - then you can decide to keep your Ttar as a Rock attacker or to TM it to a Dark Attacker.

So I'd suggest evolving it to get SD but don't use any TM's on it to get a different Charge Move. Unless it has Fire Blast.

Rock without a doubt. While Ttar's rock DPS will be eclipsed by Rampardos, its TDO is unmatched.

It's unlikely that Ttar's exclusive move will be coming back anytime soon so I would take advantage of it.