I’d say it depends on your charge moves. if you got twister or something maybe, DT since you can charge a little faster, but the longer animation time might be an issue.
I was thinking theoretically a DT might be better in some cases, though my example was a DC dragonite where my thought process was getting the DC a little fast, but upon testing, no, they get the first DC at the same time, and shields up, nite with DT dies soon after to DB. But Gyarados with same charge moves (crunch in the test case I used), DT beats DB only in the 1v1 shields senario, assuming perfect mirror, so DT’s better energy gain does provide some advantages, but largely situational.
I’d still say in general, dragon breath’s the better fast move, both in practice, and in raw stats, you have a 33% higher damage output compared to DT, while only at 10% or so loss in energy gain, as well as longer animation time. Better raw energy gain doesnt mean much If the opponent’s got a similar/identical energy cycle, but a faster animation move, since if the final fast move takes lnger to preform, they still have out energied