As a lone traveller, I would prefer any of the following:
1A/1K: Both equally good, gives you that unique feeling of looking out in front of the aircraft. However, very close proximity to the next-door seat.
2A/2K: Probably the most private seats in the house, nobody else anywhere near you
Not sure why you'd pick 3K. I think there are no circumstances where 3K is preferable to 2K.