I have used both these films quite recently at different speeds. I like HP5+ at 640 in DD-X (thanks, John Hicks). It's nice and smooth. However, at 1600, I really like the look of Tri-X in Xtol 1+1. I am a musician and take quite a few pictures of musicians at work. I recently shot several rolls side-by-side of Tri-X pushed and Delta 3200 at 1600. With careful printing, I preferred the appearance of the Tr-X. I found that I could handle the contrast, but not reduce the grain of the Delta.(posted 8687 days ago)So... the last time I got a bunch of film, I just got Tri-X and FP4+, which I really like in D-76/ID-11. Fewer choices, less to worry about, easier to visualize what I'll get. I'll save the Delta for 3200 and up.
Very subjective comparison: at conservative ratings, Tri-X seems "grittier", HP5+ smoother. When I push them beyond one stop, I prefer the look of the Tri-X. However, out of the last 100 rolls that I have shot, at least 50 have been Tri-X, Maybe 20 or so FP4+, and the others a mixture. So more practice _should_ yield better results with it.
Various expert comments to further clarify (confuse?) the issue can be found in the Anchell and Troop _The Film Development Cookbook_, and just about everywhere else.
I have tested speed ratings of some of these following
http://www.wenet.net/~halfhill/speed1.html (and speed2.html)
Maybe time for another go-round here, too.
It's nice to have the choices.