I voted for a balance, although of course that's just a generalization. I tend to think that B-plots, on their own, can't carry a longer story -- they need help from an A-plot of *some* kind. Now, it might be the kind of A-plot that is designed solely to provide excuses for the B-plot
but that's fun when it's done well. But I also enjoy good A-plots.
Smoochies can be fun, but they don't make up for otherwise lousy writing.
PJ