The one consistent thing is that, once he got past the first couple and had a choice, the current Doctor's least favourite incarnation tends to be the previous one.
I can imagine 10 not being a very big fan of 9. While 9 still had a sense of humor, he was definitely much more grounded and serious about his tasks than 10. 10 would have probably found 9 boring
Doctor, why has nobody made that pun yet?)