Grease and flour a large tube pan or 12-cup Bundt pan. Set aside.
In a large bowl, mix margarine, butter, cream cheese together until fluffy with an electric mixer on medium. With mixer on low, add sugar gradually. Then add eggs, one at a time. Slowly add flour & vanilla, then mix until combined. Batter will be thick, do not overbeat. Pour batter into prepared pan.
Bake for 2 hrs or more at 275°F. Test cake to see if done by inserting a toothpick in the middle. If it comes out clean, the cake is done. Out of oven, let it rest at least 15 minutes. Then remove from pan.
Pro tips: Make sure margarine, butter, cream cheese. Eggs are at room temp. Put a little pan of water under your cake when it is cooking to keep moist. Start in cold oven. When you put the cake in oven then turn it on.