Whatever it is, I used Tri-X at box speed in normal lighting, and got perfect range every time.
The only thing you have to watch is to not overdevelop it, because highlights do become quite dense. Perhaps that's some of the 'difficulty' some folks experience with it. Gentle agitation every two or three minutes does the trick. For those that don't think a nice 16x20 can be had from 35mm - try this dev with TMY-2 and watch something amazing happen when you pop the neg in the enlarger and go to town.