I've settled on the Ordered dither for now. I notice when printing step wedges that the Hybrid and Floyd-Steinberg dithers cause odd artifacts on a couple of the steps. They look a bit like wood grain. I'm using an 1800, so the dots are small and the rather linear Ordered pattern doesn't show on Pt/Pd. There are some new dithers around, but QTR doesn't use them yet.
On the other hand the 1800 seems to be critical about head alignment. I ended up using the manual alignment routine and running it several times. I was getting stripes at about 1mm pitch - what size are the stripes on the 2400?
There are other threads on this site about QTR, venetian blind effect, and the way the inks work together.
Ben