From personal experience I would avoid the cheaper Shimano dyno hubs (these mostly have penultimate figure 2 or 3, like DH-3N31 and DH-3N20), they have significantly more drag than the mid to high range Shimano models and the bearings are probably inferior.
my experience is not the same i have a shimano nexus 32, all the reviews on the web say it's crap, and is Shimanos worst dynamo, i have been using it about 4 years on three different bikes done 1000s of miles on it and it's still running fine,
it's powered two different supernova triple lights the new and old version also a supernova e3 pro (pants imo)
the tinterweb reviews say it has more drag when not being used that when lights are on! tbh i can switch them on or off when moving and can only tell the difference on smooth tarmac as the bars judder on cycle trail surfaces you'd never know they were on, apart from the screams of peds/dog walkers/cyclists stupid enough to look at them
also have an xt dynamo tbh there is no real world difference both slam out more than enough power to run supernova triples
save money on the hub and splash on the best lights you can afford, Supernova triple all the way for me
see and be seen
btw i bought the xt dynamo as a wheelset from germany for silly money
