I had a few 100' rolls of Neopan 400 and I liked it well enough. Mostly developed it in HC-110 or Microdol-X. I'm now working on a bulk roll of Tri-X and am shooting Tri-X a lot in 120 as well---mostly developing in D-76 and Rodinal. I've shot HP5+ off and on through the years too.
My conclusion in the end? Don't really matter. They all look good, really. With so many variables on developer, exposure of the film, times/temps, how you scan or print, etc. the looks can vary, overlap, look grainy, look smooth, and so forth.
If forced I'd say I found Neopan's grain not as tight or sharp as Tri-X, sometimes ever so slightly mushy (less accutance), but with a nice tonality. But you know what? That lack of sharp grain that I found was likely more me and my workflow than the film---and if I wanted I could adjust somewhere and gotten better/sharper grain.
All this said if someone held a gun to my head I think I'd lean slightly towards Tri-X; but if I found myself on a deserted island and only had Neopan 400 to use for the rest of my life I'd be happy enough. Just gotta try some in your workflow and see if it fits the look you want and your style.
For now I find all the smooth, less grain look in Neopan 100 Acros or Delta 100, so for my 400 speed film I desire a more "gritty", less smooth look. I like the alternative Tri-X gives me to those two.
