Honestly speaking, i really love Acros 100, the 2 rolls i did at 100 were amazing, loved it and i was looking to make it my favorite, but this film has some debates on some websites about reciprocity, and i don't know what is that, so i make it out until i understand more about it then i will think about it again.
Reciprocity failure, or more accurately reciprocity departure, in it simplest explanation simply means that the film's real speed is lower when the exposing light is very dim and long exposures are required. With some films, the effect is rather dramatic. Exposures that meter for 10 seconds will actually need 20 seconds to get the right exposure with some films. Read through the tech sheets for Kodak's and Ilford's films. They outline just how much exposure you need to add for very long exposures. Some films require an extra stop of exposure when the exposure called for is as short as 1 second.
My recommendation? Fuji Acros or TMX, and these days I'm leaning more towards Acros. I just love that stuff. I use in medium format for very low light and night time photography where it's actually faster than some 400 speed films because of its outstanding reciprocity characteristics. Not only that, but the grain is, for all intents and purposes, non-existent, and the tonality is just right. I'm very impressed with this film, and the fact that it sells for less than the Kodak and Ilford equivalents makes it all the more attractive. Fuji's got a real winner with this one in my book.
Reciprocity departure issues with Fuji Acros? Not really. Straight from Fuji's tech sheet "No exposure compensation is required at shutter speed of less tan 120 seconds." That's pretty darned impressive if you ask me, and I don't think there's another film that can beat it. Delta 100 and TMax 100 don't even come close. Delta 400 and TMY-2, while not too bad, require even more compensation. Plus-X, Tri-X, FP4+, and HP5+ all have extremely poor reciprocity departure characteristics in comparison, and IMO should not even be considered for extremely low light work unless one is forced into the situation.



