Which finger?

It's just like you to worry about something as trivial as which finger to use. If your thumb feels the most natural, then go for it. As for me, I'll dominate everything without even lifting a finger!

I use my right thumb since it's handheld, but switch to my index finger if I get tired.

It's a tablet smaller than an iPad. Anyway, it's just barely big enough to type on vertically, so I just operate it with my thumbs like that.

I'm using the stylus that came with my smartphone. It's harder and thinner than regular ones with silicone tips, making it easier to use! ...a rather off-topic answer.

I play with my right middle finger, but doing it with my thumb is harder...(*ﾟДﾟ*)

I'm using the stylus that came with my phone. It's cheating.

My dominant thumb too! I think thumbs are probably the majority~

My thumb is the easiest to use.

I'm a thumb user too. It just feels the most comfortable for me.

Basically, when I'm looking for the rest with my thumb, it becomes my index finger☺

Mine is my right index finger. I imagine people who are used to game consoles or use gamepads regularly on PC are accustomed to thumb controls, so they might use their thumbs. I personally only use my smartphone and PC mouse/keyboard, so I rarely use my thumbs for controls.