what do you find to be the most recommended cake filling or most asked for filling?

In my experience it depends on what you offer and people tend to recommend what they try and like the most. I think it'd differ for everyone.

With white cake everyone is digging the lemon curd. With chocolate, usually mocha buttercream or raspberry filling.

Raspberry filling is #1, and when they're in season, the organic strawberries take the #1 spot. Chocolate mousse is coming-up as a #1 equivalent these days as well. It does depend on the person, season, and if I'm pushing anything =)

Strawberry cream filling and real homemade fudge are my two top fillings...