it depends what you are going to use it for. i dont mix anything. i use mine to make jerky, chili, meatloaf, spaghetti, etc. i'll mix pork or beef in to it later for some recipes. my jerky is always straight ground venison.
I like my burger as just venison, I'll mix in some egg, garlic, worsh. sauce and other stuff depending on what I'm in the mood for (blue cheese crumbles, hot peppers, etc...)
Why ruin it with pork or beef? But to each their own, enjoy your success.