How to triple tongue?
You can use Da-Ga-Da Da-Ga-Da etc.
Most of students cling to the first way and, having already learned it, are naturally reluctant to change.
Does it matter?
Well, why do we use the Ga syllable at all? To give the tip of the tongue a chance to reset.
Doesn't it logically follow that that weakest note is the second of the two "Da's"?
Usually when playing a string of triplets, don't we want to put a slight accent on the beginning of each triplet? If so, Da-Ga-Da Da-Ga-Da puts you at a disadvantage.
For my money, Da-Da-Ga is the way to go. This puts the weakest note in the middle.
Of course there are those purists who use...Da-Ga-Da Ga-Da-Ga (starting every other triplet with Ga).
Well, maybe for you but for me that's just too weird.