it has to do with the variable coutner in (alpha counter in). Shuma has 2 assists where he just shoots the eyes, however his variable counters are different for both (unfortunately i cant remember what either of them are, but they ARE different). another one is Morrigan, she has two assists where they are projectiles, however the balance has her variable counter in with shadow break.
If i am also not mistaken, the team hyper combo may also be different, but then again nobody uses them so who cares.
but yea, unless you dont really care about variable counter ins, it doesnt matter what assist you pick between the two.