I found the drop rates of crimsons to be pretty much the same in both locations. The CT is more crimsons per hour as combat familiars really speed up the kill time, not because they drop them more often. Theres big differences between the cost, required levels and methods in each location. I truthfully agree with joe cuz like i was there half an hr ago and was like there for 3 mins and almost died... So Ancient Cavern is the best way to go...