I do both. Mostly singletap because i'm obssesed with Acc and x300 and don't care a lot by combos. Singletap it's much better to follow the rythm and be accurate for me.
I can singletap with any of my 2 fingers, also i can stream and do triples starting using the finger i wish. Had to relearn how to do it with the second finger. I learn with both fingers in way to do triples after slidders at high AR+BPM where i finish a slidder singletapping and have to hit next triple rigth after without a lot of time to use the same finger.
I usually singletap with the middle one. If i'm playing for to long and my finger it's sleeping or slower because it's tired i just tap using the other one a couple patterns in way to feel the rythm.
When i'm not well warmed up or without stamina i alternate before the triples/streams to cordinate better the fingers.
At high bpm spaced jumps i start trying singletap but if i can't my 2° finger finish the spaced jumps singletapping or alternate the end. It depends how fast it's.
At easy slidders i alternate upping the finger when the other it's just hitting the next, so i don't slidder break.
At technical maps it's a bad idea alternate the slidders for me because i lose the rythm after the slidders so i'm forced to singletap them if i want good acc or start well next pattern.
I singletap all stacked circles and the slower doubles. Bursts obviously no.
I alternate 100% for 1-2 years, doing all the circles like a stream. Then learn how to Singletap in way to enjoy more the game. I was doing both styles when i want for 6 months. Now i can't alternate jumps and technical patterns because i didn't did it for a long.
Maybe i'll back to relearn how to alternante in way to play DoubleTime properly. Anyways i'm not interested into the mod, only into learn something usefull playing it to export to HR/Nomod plays. Probably how i tap rigth now will be how i'm going to tap for ever.