Moderate current to little in my expierience.
I have approx fifteen in 80 gal planted tank with two eheim 2217's.
they don't much care for the extra current over the one eheim I used until a month ago, but they manage to find area's where flow is not too strong(around wood,tall sword plant's etc).
Same experience here as above. I found they move throughout the tank more if the current is either slow or diffused in some way. If I remember correctly they are, in nature, from the slow moving parts of the Orinoco river. Well, at least the H. Rhodostomus comes from that part, I am not sure about the other two types. Mine became even more outgoing as I got closer to a blackwater tank.
i am setting up a 50g sunshine pleco grow out tank and thought a school of them and emperor tetras may be a nice addition. I want to add a power head for extra current for the sunshines but maybe I will hold back on that. Are emperors fin nippers?