I'm slowly running out of my stock of APX400 and because it's not available anymore I need to choose a new "standard" ASA 400 film for me. I've been reading this thread with great interest and I even wrote down some notes! I'm using primarily D-76 or Rodinal for developing.
I guess It's time to do some film testing!
As you are testing for a new film (always exciting) I thought I may share some of my experiences with the 'big players' in the lineup.
Well, I was using APX a while back for a short time and found that although the tones were lovely (done in Rodinal 1:50) I discovered that the true ISO was closer to 200 than 400 done in this developer. In addition I have read that it is a slower film than TRI-X, so I finished with this film because if I am using a 400 ISO film I want to garner that speed. I don't want to be down a stop before the game has even started.
So, if perhaps you were to consider choosing one of the three 'big players':
Kodak TRI-X
Neopan 400
Ilford HP5
then here are some personal observations I found from souping them in both D76 and Rodinal.
Neopan 400 the finest grain of the three. It also displayed the highest contrast, hence giving that hard hitting photo journalist look.
Ilford HP5 had the largest grain and was closest to the older emulsions than the other two. The contrast was the lowest of the three. I am starting to slowly convert to this film after using TRI-X for so long. The new TRI-X seems to have lost something when it was revamped, namely that mongrel grain it was famous for.
So, Kodak TRI-X's grain was somewhere in between the other two and thecontrast was close to the Neopan 400. It also seems to be the most tolerant of exposure/developer errors (like increase in temp/time). I think that these are some of the reasons that it has been favored for so long by documentary/journalist photographers. It is also robust.
I really like Neopan 1600 but found the contrast sometimes prohibitive if using it on a sunny day. It is a great cloudy day film exposed at 600-800, in D76 1:1 for 7-8 minutes.
I have recently used Kentmere 400, but ruled it out as it seemed flatter and there was is not enough supporting literature/user feedback to change over.
I did use Lucky 100 three times and found the highlights were 'trippy'. The images seemed to more resemble the older TRI-X. I couldn't get any 400, so availability was a problem. I am still interested in drowning its big brother, the 400 in some Rodinal. I was very impressed with the 100.
I tried Rollei 400 Retro S, but the processing times are way tooo long in comparison to the three big players. I also processed for the suggested 20minutes at 1:50 and they came out very dark. This time by the way is double that given for the other three, so it doesn't seem a practical alternative. I enjoy processing like the next man, but 20 minutes seems like a stretch of the imagination, especially if you have a whole batch to do. I did read that this film should be developed in Rollei developer to take advantage of its multi-layered technology.
I liked the tonality of the new TMY-2, but found the highlights get hot easily and it is too easy to overdevelop and hence lose these highlights in the process. Also, on the street I found that on a sunny day, if the subject is in the shade and there is a strong lit back ground in the distance, these differences in zones cause that background area to go white too easily without definition retained in these highlights. TRI-X doesn't do this as readily.
This new TMY-2 is also too sharp with a modern leica lens and although the tonality is great, I wouldn't use modern glass with it again. It catches every imperfection. An older uncoated or single coated lens may fair better.
I'm not particulary fond of the new generation of emulsions like Delta and TMAX. For the street where exposure control is more limited than the studio, I think that it also sometimes pays to use the older emulsions as they are more tolerant of exposure/processing errors. Often there isn't enough time to get things right in camera, so you have to compensate in the tank and that is where it pays off using the older emulsions.
I hope these observations help. Not scientific evidence, just souped a lot of film over the last couple of years and have read others accounts as well.
Good luck!