If you have PDK, a PDK/Warlock is fun to plat. I've done all 3 types now, Fey, Fiend, and Great Old One, and have enjoyed them all.
You start at L15 with PDK starter gear, but I get rid of most of it. I use Cannith Crafted platemail to start with that has blue augment slot. I craft Greater Twilight on it (
Cannith Crafting Planner) to reduce Arcane Spell Failure.
Don't forget spell sticks or items to equip to for spell power and spell crits.
Lastly, if you Iconic Reincarnate at level 28 you get 2 nice passive past life feats for end game; PRR from PDK and MRR from Warlock.