Any bus that has the DD13 as an option will most likely also have the DT-12 as an option. Setra (Mercedes-Benz) with their imitation DD13 called the OM-471 will have that option.
The DT-12 is a much more sophisticated transmission then any of the Ultra Shifts, or ZF transmissions. It shifts smoothly, quickly (still with interruptions since it is an automated manual). But-it is a purpose built automated manual-not a conversion. It is a 4spd main box with a 3spd planatary rear splitter. The clutch engagement is very smooth, the shifts won't rock you back and forth. The two neet features is the coasting-when you're going over rolling hills, the trans will go into neutral (actually just push in the clutch) allowing free wheeling. Touch the brakes, Jakes, accelerator, and it goes back in gear. Also when backing, push hard on the brakes twice, and the transmission will creep like a regular automatic-making backing much more smooth.
Although the Allison TC10 sounds good on paper, it is an advertised twin countershaft transmission-but only uses one side at a time per gear. Freightliner will not have the TC10 for a long time. Paccar will be the first of offer it. Look to be very expensive-almost as much as a regular Allison automatic. Good Luck, TomC