It depends on the desired output, and on what kind of special processing I might need to do. If I am shooting where I might need to do one or two stop pulls, I shoot transparencies. They are way way way more versatile than print film as far as what you can do with processing to alter contrast. Try pulling a neg film 2 stops and see what happens! Slide films just get a slight cast that is correctable, and otherwise act just like a pulled black and white film.
If I want the finest possible grain, and will likely be pushing instead of pulling, I'll use a neg film.
If you want to scan, it doesn't matter that much. I suppose pos. films are technically better, but neg films do scan very well nowadays as well.
You really have to think of your desired output. For photographic prints, you might as well use print film unless you specifically want the Ilfochrome look, which is great for some things, and bad for others. For publication/printing, nothing beats giving the printer a transparency. (I'm talking traditional litho printers.) Otherwise, you'd have to print first, and they would have to do their color separations off of the print instead of straight from the original transparency. That means a more tedious process for the printer with less raw material for them to work with, and more generation loss. If I were shooting for a book, I would absolutely shoot transparencies. Otherwise, probably negs. for a series of prints.