I honestly don’t know which way feels more natural to me. If I start counting something, I’m definitely starting with the thumb. But if I’m just trying to show 3? I… I don’t know. Both seem equally valid? It’s a different gesture anyway, when counting I’d have my palm facing towards myself and when trying to order 3 beers I’d have my palm facing the person blessing me with beer. Though I usually don’t go to places so noisy that I can’t speak to the bartender anyway