Gundrak is the best for sure. I finally did heroic drak last night and yes if you do it right the last boss is very easy. But yeah, a full 5 badge gundrak run is faster than a 4 badge drak run (and faster than a 3 badge UK run!). Best farming instance for sure. I think I'm going to try heroic culling of strat tonight or tomorrow - haven't even done normal yet.