My opinion is - it all depends on what you want to do with it.

If all you are going to do is make hamburger patties, then you use beef fat.

If you are going to make sausage - then you use pork fat.

Bacon is a nice additive - down south carolina - they put bacon in deer meat along with some beef fat and it makes it taste just like a bacon burger you get in a restaurant.

The way to make good sausage is to have a recipe and ingredients that you might be able to buy off your local butcher that is the same stuff that your local grocery store uses to make their own sausage.

This is the stuff that I use
http://www.conyeagerspice.com/hunter.htm