What out of all of those was the least aggressive. I've seen a couple nice stoni and and venustus but when I had a venustus like 5 years ago he would be fine one day then next day he would be the shit out of everything and killing fish twice the size of him. I might just avoid nimbochromis completly.
What size tank are you trying to keep them in? Often in the cichlid world I think people just try to keep certain species in too small of a tank and they get an exceptionally bad rap as a result.
IMO, polystigma or linni are probably the least aggressive, but they are still need at least a 6' tank long term. Averaging all of the large livingstonii and venustus I've kept, I'd say that they are about the same aggression level, but occasionally you might find a bad apple.
As for N. fuscotaeniatus - IMO they aren't really a Nimbochromis at all and if they still are I'd be really curious to know the reasoning. A while back I recall some discussion of moving them to a different genus, as the only part of them that fits well in Nimbochromis is the patterning, while the rest would be a better fit in Tyrannochromis.
I've kept two males in the past and have a third one currently. They have all been much more aggressive than Nimbochromis I've kept, so based on your comments I'd suggest passing and looking at a different species instead.
