For the most part, a DK is harder to macro/click sequence then a Pally.
So many will drive with the DK, hitting whatever runes are not on cooldown.
There are some click macros for the DK, Stealthy has one for Unholy Tanking on the wiki.
Have not seen a click macro for a DPS DK, chances are you'd run Blood as a DPS.



I'd go with more Pallies and fewer DK's.
Basically, up to 3 Pallies get your additional blessings and useful aura's for your team.
Plus you can judge three different judgements.
A DK has quite a few melee buffs which they add to the team... but aside from a second Death Grip, an extra DK doesn't add as much as an extra Pally.

I'd probably go Prot, DK, 3x Ret.
Of your choices, I'd go with the 2nd option... Prot, 2x Ret, 2x DK.



The DK brings Death Grip, which is huge in pvp and overcomes the ranging/kiting issue in many cases.
They also have the Frost thing (sorry don't play a DK), for a substantial snare once someone is in melee range.
They add several other melee buffs to the team.

Once you already have four Pallies on the team...
A fifth lets you double up on a second Judgement in combat... you already have the buffs you'd want.
A DK brings a lot more then a fifth Pally does.

The Pallies have Divine Storm, which is a heal for the most hurt target.
And they have Art of War procs, which can be self heals or directed heals at whoever is taking damage.
That is probably the biggest thing a 5th paladin adds to the team.
But a DK has some self healing too, and brings a lot of buffs to the table.



You can grant 1 level, per even level gained.
But once you are 60th, RAF ends.

So if you were leveling 1st to 60th, you cap out at 30 levels granted (to a toon lower then yourself).
Or if you were a DK, then you only gained three levels (56th, 58th and 60th), in which case you can grant 3 levels.