No one mentioned the basic technical difference: Agfa 100 is a classic "old" tech film, Delta 100 is "new" tech film. The Delta is therefore a very fine grained product, with a very uniform grain - I would say it gives away nothing in terms of grain size to some 50 speed films like Pan F. I really like classic old tech films, my favourite in this speed range being FP4+, flexible, easy to work with and to me, gorgeous to look at (much like Agfa was). For someone who is looking to get back into film, I would suggest a film like FP4+ to cut your teeth on, as they are a little more forgiving - but if you want nice tonality and very fine grain for the speed, Delta is an excellent choice. But the main difference is not one of "better" or "worse", but rather of look.