Shadowstep's new design
In order to make this decision even more difficult, Shadowstep is undergoing significant changes in Mists of Pandaria. The percentage-based damage bonus that it currently grants our next finisher is disappearing. That doesn't mean that Shadowstep doesn't help our DPS, as it does allow us to increase our uptime in melee range. The impact is that our openers have lost some of their burst potential. In addition, the 70% speed boost after using Shadowstep is being cut from 3 seconds to 2 seconds.
To compensate for the drop in offensive power, Shadowstep will be able used on friendly targets. With this new feature, we can use Shadowstep defensively to avoid being trapped, and we can also use it to quickly assist another friendly player. Shadowstep is shedding its previous damage bonus in favor of additional utility, which unfortunately increases the commonality it shares with Preparation.
It's not about damage
With Overkill gone, assassination and combat rogues won't gain a single point of DPS on most encounters via Shadowstep or Preparation. Our decision will be based purely on the utility of each ability. Unfortunately, rogues don't have much experience in this department. The vast majority of our talent, gear, and character choices revolve around damage. DPS is the constant that we can always align our decision-making compass to.
In fact, this choice probably won't involve PvE at all. We can always swap between Shadowstep and Preparation on a per-encounter basis. There's plenty of downtime between bosses, and it's common for players to optimize their setups for any given boss. If you need defensive cooldowns, then Preparation is your best bet. If there's lots of running around or target swaps, then Shadowstep becomes more valuable. I don't think we'll have much trouble picking the right talent for PvE.
Utility and PvP
The problem with trying to make objective decisions about PvP is that it's so nebulous. You never know what classes you'll run into at the Lumber Mill or which specs you'll be facing in an Arena match. PvP fights are anything but scripted. While we can explicitly plan to use Shadowstep to counter a boss' particular ability, there are so many abilities and counters in PvP that we're incapable of solving every possible outcome.
If we take Preparation and Shadowstep at face value, we can find the utility of both abilities. Preparation allows us to front load a ton of offensive and defensive cooldowns, but only every five minutes. Shadowstep gives us a much more modest boost to our mobility, but we can Shadowstep more than twice a minute. The key value of Shadowstep is that it allows us to close gaps constantly, while the value of Preparation is the ability to exploit multiple cooldowns to overwhelm our opponents.
Melee and ranged
Against melee classes, Preparation is the clear victor. An extra Dismantle and Evasion can easily turn the tide of an encounter, and that's not even the potency of a second Vanish-based opener. If we're facing off against a single melee opponent, chances are that neither one of us will be running away. Shadowstep's key function is to increase mobility, but that's not a major concern of ours when fighting other melee classes.
The value of Shadowstep is seen when facing ranged opponents. Their first priority when fighting a rogue will be to run away, since rogues are only effective when in melee range. They'll try to kite us with every snare, stun, and speed boost in their toolbox. Shadowstep allows us to close that gap quickly and repeatedly. Fighting a ranged class is a constant positioning tug-of-war, with Shadowstep tipping the scales in our direction.
Preparation is still quite valuable when fighting a ranged class. While Dismantle and Evasion are obviously nearly pointless, Preparation also resets the cooldown on our Sprint and Cloak of Shadows abilities. Sprint and Cloak are two of the most important tools when it comes to handling ranged classes, and Vanish is similarly valuable. Preparation is versatile enough to provide value against opponents of any type.
Burst vs. sustained
While Preparation might look like the obvious favorite over Shadowstep, it does suffer from one key drawback: We can only use it every five minutes. It's only one extra Sprint and Vanish, or one more Evasion and Dismantle. In a short battle, that type of cooldown saturation can be very persuasive. If healers aren't involved, it's likely that the fight will be over before you can even use all of those CDs. However, if your opponent handles your barrage of CDs with ease, then you're left without that talent's benefits for five long minutes.
Shadowstep, on the other hand, can be used regularly. If you're playing a long game of cat-and-mouse with your opponent, then you're going to need multiple gap closers. With healers supporting both you and your targets, you'll be able to use Shadowstep multiple times, while Preparation would simply sit on cooldown. Shadowstep allows you to constantly be attacking your opponents.
I think Preparation is going to give us the biggest benefit in most PvP situations outside of Arenas. Shadowstep is definitely a contender, but will probably be saved for specific situations where a barrage of cooldowns won't turn the tide of a battle in our favor. I'm still upset that rogues have to choose between these two iconic abilities. We've been asking for Shadowstep to be universal for years, and it's bittersweet to see it available in the talent tree but placed on the same level as Preparation.
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