Really, there aren't any bad F seats in CX's 747.

For privacy, 2A/K are probably best. (1A is vaguely close to 1K; the row 3 and 4 window seats are vaguely close to the row 3/4 center section seats.) However, for space, the row 4 window seats are best because you've got a wide shelf between the seat and the window.

If I'm traveling solo, the seats I'd prefer least are the center section seats and 1A/K -- I don't care for the latter because (for me) the proximity of the bulkhead prvides a much less roomy feeling than the other seats.