NOTE: Updated for 4.0.1
From the limited data WordPress provides me on Google searches that lead to my blog, it seems people want to know what runeforge they should be using for DPS.
USE FALLEN CRUSADER.
The reasoning behind using Fallen Crusader over the other enchants is that the +15% strength it provides (it was nerfed from 30%, but its ppm [proc per minute] was increased, which greatly increased its uptime) affects ALL the spells and strikes a DPS Death Knight will use. Cinderglacier and Razorice have a narrower scope and so are generally less useful.
For Frost Dual Wielding, you should be using Fallen Crusader on OH and Razorice on MH. Razorice on MH stacks it faster, while the proc rate for Fallen Crusader on MH/OH is the same.
Tanking is a different ball game
Stoneskin Gargoyle is the optimal choice here. 4% armour and 2% stamina? Yes please.
PvP is another metaphor describing how it’s different, almost like it’s a horse of a different colour
For BGs, I would suggest using Fallen Crusader due to the damage and healing. In arenas, however, Swordshattering is worth consideration due to cutting disarm time in half. If you face a disproportionate amount of warriors and rogues, Swordshattering could be a boon and worth losing the DPS/healing of Fallen Crusader. You’ll also get more Rune Strikes from the extra parry chance. That said, this is really only a good option if you know that you face more melee, especially rogues and warriors, than other classes. Against spellcasters this rune goes to waste, which is a large downside.
Spellshattering is simply not worth consideration. 4% spell damage isn’t all that important and you’ll most likely never get silenced, especially if you play with a healer as a partner. Mages/Spriests who think outside the box, or even opposing DKs might silence you on occasion, but it’s not threatening enough to be worth runeforging to prevent.