Exactly. Ten fondly remembered being Five, while Six was relieved to no longer be Five. Third and Second bickered like an old married couple, and First looked on both with disdain. The Doctor isn't generally a fan of himself. I think Ten liking Five is the exception.
I think this is a very hard question to answer, as its unlikely you will ever have all the Doctors in one form, being able to speak for all of them. When it aired, the Doctor clone in The Almost People, seemed to not like being Ten, saying "weve moved on" (or similar)
What an almost meaningless question. But I'll say The Eighth Doctor, for the joy he felt wearing those shoes.
The First did seem to take a shine to Five, IMHO, in The Five Doctors And...The Master seems to have been sweet on them all, except maybe 1, 2, (Yes, The 5 Doctors and schoolmates) 9 and 11.
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 think we need to look at this from a timey wimey perspective. When all's said and done, when all his past and future regenerations are considered there really is only one choice for which Doctor he loved being the most.... The ginger one
4 and 10 seemed to have the most difficulty coming to terms with their impending regenerations. This may be partly because both knew in advance that the end was near, but they both seemed to really like the time they were having and didn't want to go. Others like 3, 5 or 9 seemed resolved to their fate.