Specifically for LOD encounter it really depends on whether you do 0% or 30% or something more "spicy" as a challenge. Intellect is the best stats for Holy Paladin - more you have more mana pool you will start with and more mana you will return during the fight via effects like Replenishement, Divine Plea, Mana Tide Totem, Rapture and Revitalize. Intellect also increases your spell power via talent as well as your spell critical strike chance. Bis Hpala has around 1150 haste raiting which drops his Holy Light cast to about 1.19 sec with all raid and self buffs. Additional elixir and food for haste will drop it to about 1.17s range. Going for more haste raiting past this value wih gems basically means you have to sacrifice more effective stats. While Haste scales linear, Haste Raiting actually hits DR as a stats which means that if normaly it requires 300 haste raiting to drop your cast time from 1.3 to 1.2s or -0.1s, it will require 400 haste to drop your cast from 1.2 to 1.1s or the same -0.1s aka more your cast time is closer to 1s GCD cap, more haste raiting will be required for the same amount of cast time drop. This is because 1% additional haste means you will do 1 cast more for the time it requires to do 100 casts (this is where linear scaling of haste comes). Anyway more haste also means you will cast faster => you will spend more mana. All of the haste holy paladins basically suffer from the need to autoattack the boss very often to return mana via Seal of Wisdom and Judgement of Wisdom which sometimes can lead to fail especially during second phase of LK 0% when tank is getting big spike damage and paladin runs out of mana and have to stop heal and autoattack the boss. To summary everything, as a haste holy paladin you sacrifice about 8k mana pool, 4% critical chance and 100 SP just for the drop of your cast time from ~1.17s to 1.05s. As a holy paladin your main job is to keep tank(s) alive. This sometimes requires from you to chain cast for long period of time which basically it's impossible as a haste holy paladin unless there are enough druids to feed him with Innervates or another sources of mana gains.
I personally have some items to swap with haste for really fast bosses or bosses where I have time to regen mana via autoattacks (for example Sindragosa during Air Phase where I can safely use Divine Plea and return mana via auto attacks) thus I can add around 100 haste more and drop my cast to about 1.14s but for LK I always stick with haste from gear only + haste from elixir and food.
Conclusion: Stick with Intellect. This is what the class has been ment to be on progress and late game.