I see some people use their pointer finger to single tap but I personally use my middle finger. I'm just curious about other people's play style. I find it hard to switch from streaming to single tapping or vice-versa when using my pointer finger.
Index finger almost always. Sometimes I swap to my middle finger if I'm running out of stamina single tapping with my index, though. If I'm failing a specific pattern over and over I swap to my middle finger I can sometimes do the pattern more consistently... I have no idea how it works (wouldn't be surprised if it was a placebo effect or some bullshit) but it works. Maybe it's because I'm no longer playing with muscle memory? Not sure.
Since I was young, playing arpeggios on the piano was easiest for me when done from pinky to thumb, and not so easy from thumb to pinky. It's the same even for just 2 fingers (index and middle), so I prefer to start with my middle finger on all patterns. I lost interest in piano quite early on though, my sense of rhythm was awful... Still is
My middle finger is also stronger and can stand wrist taps for much longer.