Preheat oven to 325 degrees F. Thoroughly grease fluted pan or a regular 10-inch tube pan.
Beat together margarine, butter and cream cheese on medium speed until well mixed. Gradually beat in the sugar and continue beating for 5 minutes.
Add eggs, one at a time, beating well after each addition. On low speed, beat in flour until well blended, scraping down side of bowl as needed. Stir in vanilla.
Bake in 325 degree F oven for 1 hour 20 minutes. Cool cake in pan on wire rack for 15 minutes. Remove cake from pan to wire rack to cool completely. Dust with confectioners' sugar if you wish. Makes 16 servings.