I go with the whole hand. I'd like to be a 2 finger person but I worry about not getting it right and looking weird. You have to keep your fingers together if you're using 2.
Just thought about it this morning as I was at it non stop down the 15 mile one lane road to Loch Etive.
So how do you thank other drivers? Anybody do the grin and 2 thumbs up "fandabidozy" style?