op, wear whatever gear is itemized correctly for you. whether its cloth, leather, mail, or plate doesn't impact you until level 50 when you learn plate specialization. most people do not receive this bonus until very late into the game as there is only one plate-intellect heirloom in the game. holy paladins leveling with heirlooms will be wearing cloth, leather, or mail until 85. the 5% intellect bonus is not a huge deal, especially at a lower level. also, there are not many plate-intellect items around while leveling and you'd likely have to wait till your 60s or 70s to finally have all plate-intellect items if you're leveling without heirlooms anyways.