Newbie question here...
I have used both TMAX (100 & the old 400) and also Delta 400 35mm roll film, and dont really see much of a difference.
I have been develloping both with the same chemicals (TMAX Dev, Ilford Rapid Fixer and Kodak Hypo and rinse aid) and apart from slight dev time differences, they both appear about the same to my (untrained) eyes...

What is the difference between the 2?
Is 1 better than another for certain conditions?
Why would you choose 1 over the other? (excluding cost)

I'm trying to decide which film to commit to using long term as I think using different types may slow my learning down untill I fully understand each different film.