I also voted for a good balance.
My reasoning is this: a fanfic has to have a good, rounded B-plot to satisfy me. Most longer fics need something in the way of an A-plot, too, though it doesn't need to be as solid. But that doesn't mean the A-plot is taking second place; an A-plot with gaping holes will wreck a story just as quickly as a weak B-plot, maybe even quicker.
So a fanfic needs a good balance between A- and B-plots... but that doesn't have to mean equal time for each. A good balance could be a minimal A-plot in the background and a strong B-plot occupying centre stage.
Mere
