The X in APX25 & APX100 designated them as newer technology films, much later the X was added to APX400 but this was still older technology & the name was changed to match the range of Agfa B&W films.
APX100 was always as good as Tmax100 (if not better) while having a true effective 100 EI, while Tmax100 needed to be used at 50 EI to get similar results. I stopped using Agfa films when they discontinued APX100 sheet film.
I have quite a bit of APX 100 in 120 in the freezer and I have used it side by side with Tmax 100 a lot of times and they are indeed very comparable. In my Beutlers process they both end up with finer grain than Acros or Delta 100 or even Pan F. The reason I have switched to ACROS and Tmax 100 is reciprocity.
This discussion makes me think of the 'old' days when all I used was APX 100 & Rodinal, along with the odd roll of Tmax 100. Then when Agfa bellied up I switched to Ilford FP4+ & Pyrocat, then I started using Tri-X because I took a liking to grain. Then Tri-X in Edwal 12 and Xtol, and now it's Tmax 400 & Xtol. The latest combination I've only used for a while, but it gets me the fine grain of the past, the reciprocity of Tmax 100 (almost, and two stops faster), and tonality that I love.
Unless something becomes unavailable, I will look no further. But the APX films were exceptional indeed. And I would not have switched from it had they not gone under.
To the OP - Keep shooting Neopan 400 if that's what you like and what you're used to. It's fun to experiment once in a while, but it's always best to keep things consistent. You vision and your technique are much more important than the film.
"Often moments come looking for us". - Robert Frank
"Make good art!" - Neil Gaiman
"...the heart and mind are the true lens of the camera". - Yousuf Karsh
This goes to bit OT, but i was fan of APX25 at 120 size until the end of agfa bw films.
Now, many years later i still miss the tonality thau APX25 gave with rodinal 1+100.
Now I am looking for a film with similar charasteric for 120 and 4x5.
Any good suggestions?
Efke 25 is a film I really liked, but it's plagued with QC problems; at least the 10-20 rolls I shot. I got some great looking negs in Rodinal and Pyrocat HD, but you have to take 2-3 shots of each photo to make sure you get one frame that is without problems.
Ilford makes Pan-F which is an ISO 50 film. The QC at Ilford is great and this film is great, although it may take you several rolls to get your EI and processing routine set.