I should have said, for me, I think I'll go with:

4,3,1,2,6,5

I just love the whole Drago thing in 4, the way Rocky must return to hardcore training (including the sit up whilst hanging from upside down from a rafter) the acting was poor, probably the worst of the good ones, but I just loved the cheese of it.

3 is sometimes my favourite, but it was the change to the more commercial side of Rocky which loses it points.