Spectral sensitivity is definitely different. Delta looks more like a traditional B&W film, and TMax looks more like B&W video in this regard.

Personally, I prefer Delta 400 to TMax 400, but I like TMax 100 (because it's so sharp) better than Delta 100 (because the tonality is kind of bottom heavy to my eye), that is when I'm not using Tri-X or Efke 100 or FP-4+, which are my main films of late. If Delta 400 were available in sheet sizes, I'd use a lot more of it.