Shoulders (badges) and Chest (S.K. shards) both give a 10% boost to experience.
Combined, you only need 81% of the normal experience to level.

Unless you have the resources for cloth, leather, mail and plate versions, I'd go with the cloth.
Then you can use them for any team, on either faction.
And you can do a character transfer (with the items equipped), if you want them on another server.