Definitely pinkie to index, with both hands. I remember my mother teaching me to do this when I was still a toddler.
I never really thought about this until I brought back a beautiful pair of castanets from Spain. When “drumming” the fingers, it’s pinkie first, but the hard part is that you need to “un-click” each finger before clicking the next, otherwise you’ll hear only the pinkie clicking. Not as difficult as, say, playing the violin, but harder than you’d think.
Pinkie to index here - all other methods are wrong, even though I can do index to pinkie if needed.
Index to pinky. Sometimes index to pinky then backward, and so on. But I always start with my index finger. Pinky to index isn’t as easy and I really do more of a pinky-ring finger drum on the return because my right pinky lacks range of motion.
I opted for the third option, though I can go either direction equally well [played clarinet and electric bass, FWIW] however I do not tap in order, I tap musical fingering sequences. Typically fingering for whichever song is my earworm that moment.
Pinkie to index? Who are you weirdos? shudder
I didn’t know this was a thing. If I’m “drumming” with my fingers, I’ve got one finger per hand out. Or, since I’m a piano player, I’ll sometimes do it one handed with my ring and index fingers. When I’m just idle, I’ll either go both ways, or play songs. Or even just improvise on an imaginary keyboard.
I guess that pinky to index is easier, as it’s easier to start on the ends than in the middle. But thumb to pinky is the easiest because I have a lot of practice “rolling” chords on a piano.
Put the wrong answer – I actually drum from pinkie to index/thumb, and not how I voted, which was the reverse direction. Don’t know why. FWIW, it’s generally considered easier to play a quick descending scale on the keyboard than ascending, at least it’s general to me. Not a big finger drummer myself – like to use the whole hands and get all Bonham on it.
Indeed, and even worse they outnumber us normals 4-1!
I used to do it pinkie-to-index until the last time we had a thread like this, and I spent so much time trying it both ways that now when I do it, I alternate! Pinkie-to-index, index-to-pinkie, pinkie-to-index, index-to-pinkie.
I start with my pinky on my left hand and the index finger on my right hand. 
FWIW I played flute and piano when I was younger, neither of them very well…
Right-handed, non instrument player.
(dabbled with flute and clarinet, but hated playing twinkle, twinkle, little star over and over…and over)
Right hand, pinky to index feels more right but can easily drum either way.
(index to pinky seems more of a blatant ‘I am showing you how bored I am’ gesture.)
Left hand, definitely index to pinky, pinky to index is far more awkward.
I am a both-ways-alternating sort of person. Sometimes I include the thumb, sometimes not. My favorite way is three fingers in succession, then back a finger and three more, (i.e. thumb-index-middle, index-middle-ring, middle-ring-pinky) and back again going the opposite direction.
FWIW I played the piano when I was younger and am trying to learn to play the guitar, although I am not very good at either.
A related thread: