For heroic I don't think anytihng beats a warlock. I'm doing 3 skulls easly, sometimes I die because I'm not used to not zerg, but with time this should correct itself. Managed to solo some quests on 4 skulls, it's very risky and not really worth it because it is a lot slower and risky than 3 skulls.
I mean solo, but always use a hire. You get somewhat good at controling them. Always do quests at base lv +1 or at base lv if possible. You get a lot more reaper xp doing that way. Diplomatic Impunity for example gave 1125 reaper xp at lv 12, with 4 skulls, using a 20% xp pot. The quests on 4 skulls I was doing at base lv +1 were giving about 800 with the same pot. For comparison, I couldn't do Frame Work on 4 skulls, so I did on 3, and it gave about 900 experience.
That means doing the quest at base lv is worth more than doing it one skull higher. Yes, despite the DEVs saying the penality started at base lv + 2, and that it was something like 10%, it seems 1 lv above the base lv you already have penality, and it's about 30%, and more 30% for every lv above.
https://www.ddo.com/forums/showthread.php/483257-overlevel-clarification#post593...This ^ is very wrong, and they know it, and don't want to talk about it