For fine grain, I'd go with T-Max 100, Ilford Pan F+ 50, or Efke KB25. (I've not tried Fuji Acros 100 or Ilford Delta 100, but my understanding is that they're both T-grain ISO 100 films, and so should be quite fine-grained, too.) Of course, fine grain isn't everything, and in some situations bigger grain is good. For grain that's visible but looks good, I like Foma products, but of course others might have other opinions. Note that Fomapan 100 is nowhere near as fine-grained as T-Max 100 or the other films I've mentioned; it's just got grain that I like, as opposed to grain that I dislike (such as T-Max 400 grain, which I consider ugly).