I think we need to differentiate between general characteristics and observations that result from specifics that result from variables such as developer, type of dilution and type of agitation.
Acros is neither a harsh or soft film, if those terms are used to speak of contrast. In general it may take a bit longer in the same developer to reach as much contrast as TMAX-100, but one can adjust time of development to give almost idential contrast with both films.
In terms of curve shape, Acros has a very straight line response, very similar to that of Tmax-100. There is very little toe or shoulder, which requires good control of exposure and development. In this sense both Acros and Tmax-100 are quite different from a film like TRIX-320 that has a very long toe.
Tmax-100 and Acros are about equally sharp, IMO, when compared with the same developer and type of agitation. Across has slightly finer grain to my eye. I don't care for the "character" that comes from grain so the very fine grain of Acros is a big plus for me.
There is a slight difference in terms of spectral sensitivity in that Tmax-100 has slightly more sensitivity to red light. However, I think most would be hard pressed to see the difference between the two films in most situations.
I use more Acros than Tmx-100 because of the superior reciprocity characteristics of the former. I have also found that Acros is usually less expensive than Tmax-100 where I buy film, though that may not be true where you shop.
Sandy King