Nah, it only depends on what you get used to, both index and middle are okay, and if you use both and play alternating them it's cool too but it's a hard technique that takes more time to get used to (Maybe not that much if you start to play since the beginning like this), which is used by these who aren't fast enough using a finger only in the songs that are required to tap fast, then by alternating you save some stamina and maybe some speed.