First of all, there is the PvP vs PvE team.
If you are specifically looking for a gear rating for higher power leveling then (as long as they are of the same level) an epic outperforms a rare one without question, in most cases. That doesn’t mean that you can equip the first purple you come across. In addition to considering your game and the stats that are best for you to level up, you should consider whether the gear is designed for PvP or PvE play.
When on the battlefields or in the arenas, most PvP players will agree that your two most important stats are Stamina, which increases your health, and Resilience, which decreases the chance of getting hit with a Critical Hit, regardless of the class you play. Other statistics are considered secondary to these two. In fact, you’ll only see Resilience on PvP gear.
Are PvP epics good enough to use to level the power in raids and higher instances?
Often this will depend on the group you are with. Much of the arena gear has stats that will work for PvE play, though stamina is pretty useless outside of PvP play. However, most players will agree that the team that falls from the higher-level instances and raids outperforms the PvP team every time.
What equipment should you be looking for?
Basically speaking, with power leveling, the higher the level of the item, the better it will be for you. Most groups are looking for players who have reached at least the Higher armor rating achievement, and gear above item level 200 is preferred. Most power leveling players will also work towards a full set to obtain optimal results.
For PvE, you will be looking for level 7 and level 8 raid gear.
Level 7 can be found in the normal and heroic versions of Archavon the Stone Watcher, in the Vault of Archavon, Obsidian Sanctum, and Naxxramas. The normal version is called the Heroes set and the heroic version is called the Valorous set. Tier 8 sets can be found in the normal and heroic versions of Emalon the Storm Watcher, in the Vault of Archavon and Ulduar. The normal version is known as the Valorous set and the heroic version is known as the Conqueror set. These are currently the best PvE sets in the game.
The best sets for PvP.
For PvP, the best gear to look for is the Season 5 Gladiator Set that can be purchased with Arena Points. There are 4 versions, they are Deadly, Furious, Hateful and Savage. These are currently the best PvP sets in the game. Meanwhile, there are also some rare Resilience Sets that can be crafted or purchased from the Auction House. While these aren’t as good as the epic gear you can earn, the set bonuses can come in handy while saving the honor points or marks you need to buy the best gear.