it all depends on alot of factor.
if ur guild have less rogue / feral , u get higher chance to get BiS Leather Gear

BiS leather gear :
more crit % than BiS plate
less ap than BiS plate
less sp than BiS plate
recommend use JoW ( if theres more than 1 pally in group)

BiS plate gear:
low crit % than BiS leather
more ap than BiS plate
more sp than BiS plate
ur JoL overwrite others JoL even if they have Divinity 5/5

basically BiS leather dps is higher than BiS plate in alot of boss fight but in aoe fight BiS plate Owned
and when cataclysm hit, there will be Plate / Leather Specialization

and the most important thing , if u play Retribution Pally u cant have other dual spec. Its either Aura Mastery and Divine Sacrifice which both are Ret tree.