Never say never! I used to think drop riffles were the best too, until I tried the fluidized bed sluices (bazooka gold trap is the newest name for a fluidized bed sluice, since they own the Schmidt patent) and moved twice as much material with almost the same gold recovery! Some claim the gold recovery is the same, but I have tested tailings extensively and noticed some fine gold loss using the fluidized bed sluices, especially under certain easily reproduced conditions (These conditions are too much water flow and excessive drop. Either one of these combined with a stock bazooka grizzly will lose fines, because the larger 5/16 gravel the grizzly allows can form a kind of false bedrock that blocks fines from settling and some of the fines will flow out of the sluice along with the slurry. Changing the grizzly to 4 mesh helps cure the problem, but 8 mesh works even better). However, the fluidized bed sluices move so much more material then a conventional sluice that the loss in -100 mesh gold more then makes up for it.
I have 14 sluices right now in my garage, and 11 of them are for sale...Besides my DIY custom fluidized bed sluice, I am keeping one small drop riffle for low water conditions and backpacking, and the other sluice that's left is the bazooka gold trap that belongs to a buddy of mine so I cant sell it!