Sitting and walking for sure, my characters are talking a lot, either by a cup of tea or while going somewhere. I try to switch the perspective up, zoom in / out etc to make it less repetitive, but yeah, still the poses I draw the most.
And to be more exact, I think one I draw THE most is sitting / standing but with this hands gesture:

...OR this one:

Sometimes I even have them on the same panel
As for 'what´s a pose which is difficult for you to draw' question, for me it's fighting poses! First it's difficult to make some kind of a choreography for a fight, then drawing it down while still being able to show movement! I have to admit, I still have to practise that a lot
This page and the whole fighting scene that comes afterwards was a hell to draw for me: